Michaud is pro-life, and knows he'd be at a huge disadvantage in the Dem statewide primary (Portland is very socially liberal); if anything, Rhode Island is more likely to elect a pro-lifer than Maine is. I don't think Michaud will jump in.
Allen will be a formidable opponent, and if '08 is a repeat of '06, the RINO Collins will lose. But I think the tide will turn before '08 comes around and that Collins will be reelected, albeit not as comfortably as against Pingree in '02.
BTW, as crappy as Collins's voting record is, she's Vernon Robinson compared to Lincoln Chafee. I think conservatives should hold our noses and support Collins's reelection.
With Rudy or Mormon Mitt on the top of the ticket, I think Collins will be insulated from any Blue Thunderstorm. Collin sshould be thankful that she's running in 2008, not 2006.