Remembering back to 2007, the thing that stands out most for me was the utter certainty of the Socialist Party that not only Comrade Joe but also Clare Daly, Mick Murphy would be elected ('ducks in a row' i remember reading).Up until the last few days of the 2007 election Joe Higgins was potentially ahead of Joan Burton. The squeeze to FF in working class areas in the last week did impact on the vote of Joe Higgins (and Clare Daly) as it did with others (like SF).
However, in order for the LP to win two seats ahead of Joe Higgins would require Joe Higgins to lose more votes and the LP increase their vote by 2.5 times in the constituency. The LP could potentially double their vote in many Dublin constituencies - but will have trouble doing that where ever the is a strong established left-wing candidate.
Many people switched from Joe Higgins in the closing days of 2007 election on the assumption that he was safe and have repeatedly indicated that they regret their decision. Furthermore, Joe Higgins will benefit more than any other candidate from the Rivervalley vote in Swords (where Clare Daly has repeatedly won a substantial vote). I also disagree with your assessment about where the slippage in Lenihans vote would go - Joe Higgins picked up about 8% of Lenihans surplus transfer last time out (compared to 10% for Varadker and 12% for Burton) but, more importantly, picked up as much of Gerry Lynam's vote as Varadker or Burton and significantly more of the SF vote.
The Socialist Party is never complacent about any election and acts accordingly - elections are nothing if not unpredictable. However, it would be a major surprise if Joe Higgins was not elected in Dublin West. If he gets the 7,000-8,000 you mention above he will be elected comfortably. The LP could win two seats in the constituency - but of they do it will be Lenihan's seat they take.
They were 'squeezed' (a good euphemism that) or people now regret their decision or were afraid. Rubbish. Every time Joe Higgins appears on television now he loses votes (the workers this, the workers that- Joe,we're all bloody workers!)
We can't afford undergraduate politicians now more than ever. FG to take 2 seats here