Analysis:  In 1926, Éamon de Valera found himself on the wrong side of a narrowly decided vote by Sinn Féin to continue its policy of abstention. He and his closest supporters (including Seán Lemass, Frank Aiken, Seán MacEntee and Seán T O'Kelly) met regularly in his house that year planning a new organisation.

They arrived at consensus quickly and within a month had set out the kind of organisation they wanted and where it would stand in the political spectrum.

For his part, de Valera said that most Irish people still wanted a United Ireland.

But cognisant that it would not be achievable in the short term, he and his colleagues were convinced that “people can be banded together for the pursuit of that ideal if a reasonable programme based on existing conditions be set before them”.

And so out of that first meeting in Dublin’s La Scala Theatre later that year emerged the seven aims enshrined in the Corú, Fianna Fáil’s book of rules. Obviously, they included the aspiration of a united Ireland; the restoration of Irish language; a social system that afforded equal opportunity; the distribution of the land of Ireland to allow as many families as possible to be rooted in the soil; and a huge emphasis on Irish sovereignty and self-sufficiency (almost isolationism).

The one-time political editor of this newspaper Dick Walsh varied a Rooseveltian term to describe de Valera's change of tack: he called it the New Departure.

Anybody who looks at where the current Sinn Féin is at now will be struck by the strong parallels with Fianna Fáil in the middle 1920s, both in the nature of the journey and in the aims underpinning the party.

Allowing for the marked societal changes over decades, there are many Corú elements to Sinn Féin's current set of political aspirations. The obvious ones relate to unity and the Irish language. Equal opportunity is also there, but then it's a stock phrase of all parties. Its agriculture and fisheries policies yearn for a return to a more simple agrarian society – where it argues to "lessen the amount of bureaucratic control by Brussels" and urges "farmers and fishermen to return to co-ops". There is an innate and visceral suspicion of Europe evident in its various political documents (and evidenced by its stance in all EU referendums). It chimes with the Corú's desire for self-sufficiency and for isolationism.

But the parallels only bring you so far. Sinn Féin is not experiencing a New Departure, rather a long drawn-out process of change – mainstreaming, as we inelegantly describe it.

As evidenced by the rapid growth of Fianna Fáil from 1926, a large swathe of the population shared its vision, believed as it did that the party was pursuing a reasonable programme based on existing conditions. The party emerged during a period of great flux and volatility in the aftermath of the Civil War, where all political parties were grappling as they tried to identify a new State. In addition, by setting out its Corú (and by accepting the oath) de Valera’s breakaways were giving validation to the new State (without stating it) and doing the same with conviction.

You cannot really say the same for Sinn Féin now. Values change and evolve over time, and what seemed reasonable in 1926 might not sound so reasonable now. In addition, Sinn Féin’s increasing incursion into representative politics (in the South) comes 90 years after Independence, with questions of identity and definition long settled in the South. And has Sinn Féin truly given validation to the State with that kind of conviction?

There is no doubt though that the party is on a journey. As far back as 2000 (when the party had only one TD in the South) a party strategist Jim Gibney was predicting that Sinn Féin’s number of Deputies would be in double figures by this decade. That has happened but not as smoothly, or as seamlessly, as its progress in the North – and definitely would not have happened if the previous coalition had not imploded so spectacularly.

A number of years ago (it must have been before the 2007 general election) then taoiseach Bertie Ahern was asked if Fianna Fáil would consider going into government with Sinn Féin. He likened the party to Democratic Left/theWorkers Party in the early 1980s, indicating that it was at least a decade, maybe 15 years away from government. I think he was right. That suggests 2016 at the very very earliest but most likely early next decade.

There is a common perception that Sinn Féin needs to be more mainstream, to put its murky past behind it, to become more acceptable. But the party has a bigger problem than that. It needs to define what it is in the South. At the moment it is a hybrid of Northern republicanism and a not fully thought-through socialist party in the South. In other words, it does not have a reasonable programme based on existing conditions.

As it starts its ardfheis tonight, it does so on the back of an increase in opinion polls since the general election (which in itself was a triumph for the party). But like the Greens and the PDs before it, it should not lull itself into believing that it's all electoral ladders and no electoral snakes.

And there are a couple of major questions that the party needs to address if it’s going to transform itself from a niche party to one of big four.

The party has worked on policy. Its pre-budget submissions have improved substantially in quality since the innumerate back-of-the-envelope jobs of a decade ago. Peadar Tóibín also produced a very well researched and written jobs policy document recently (though it relied in part on funds that weren’t there). And Caoimhghín Ó Caoláin has been a credible spokesman on health over the years.

But there are huge policy gaps there. On the party’s website, there is a paucity of detailed policy. The huge area of the environment gets all of three paragraphs; the main policy papers on health date back to 2006; as does its main education policy. The European section has not been updated since 2009, as it refers to “last year’s Lisbon Treaty”.

They lack detail, huge amounts of it. The party’s finance policies (and it’s not the only Opposition party over the last 10 years affected by this phenomenon) include a lot of wishful thinking (a wealth tax based on out-of-date and tendentious data that purports to raise €800 million per annum).

But elsewhere the party calls for universal free healthcare and ditto in education. It states it wants a State bank, a State insurance company and for State control in the areas of fuel, IT, health, transport and education. It says it does support the private sector but is against an over-reliance on foreign direct investment, favouring home-grown indigenous investment. If the party ever came into a government-forming scenario, it would have to explain how all of this would add up.

As is the prerogative of Opposition parties, Sinn Féin has opposed existing measures without fully spelling out alternatives. It presents itself as the main party of Opposition, the main anti-austerity party, and as a party of protest. It opposes the property tax, water charges and a plethora of other measures. Some would view this as opportunism and argue that its appeal to voters will be limited in the absence of alternatives.

Is its leader Gerry Adams a problem? If you ask around Leinster House, the consensus from other politicians and from commentators is that he is a liability. But there's a disconnect there, in my view, between the Beltway and the wider community. Sinn Féin supporters adore him and he has a huge cachet and recognition, reflected by high opinion poll ratings. Sure, he seems at sea sometimes dealing with Southern policy areas but you have to agree with the strategist who says he is "underestimated by our opponents".

There were some other areas where Sinn Féin was perceived as weak. Its support base had a fair quota of young blue-collar males. The party has worked hard making itself more accessible and amenable to women. It has also relaxed its strict and archaic membership rules (you had to be prepared to sell An Phoblacht ) and introduced membership cards, in an attempt to broaden its appeal to people who would be sympathetic to the party rather than dyed-in-the-wool activists.

Towards a New Republic is the theme of this weekend's conference. More accurately, it is towards a new Sinn Féin. A lot of its younger members have no memory of its violent past, yet that remains the predominant image of the party. Jaws still dropped when they heard Gerry Adams, seemingly without irony, say of Margaret Thatcher: "Here in Ireland her espousal of old draconian militaristic policies prolonged the war and led to great suffering."

There was a rare old shouting match between the pots and the kettles after that one.

Still, the party is on a long-term upward trajectory. It's not even, or all that quick – as the Meath East byelection and the flatline election of 2007 remind us. Will the aspiration of a united Ireland fade as it did for Fianna Fáil? Will the party's self-styled brand of pragmatic realistic left-wing republicanism be enough to allow it capture the citadel in the South as it did in the North? Its main problem is that Fianna Fáil is still there, and it did all that 87 years ago.