You forgot Maine's state primary on June 10. There's a 6-candidate Democratic primary for Maine's first congressional district seat that Tom Allen is giving up to challenge Senator Collins, and a contested Republican primary for that seat as well at this point although I wouldn't be surprised if Charlie Summers drops out before then. There will likely be some competitive primaries for Legislative seats that party has a chance at, like in termed out Republican Karl Turner's State Senate seat in Portland's northern "cruel yuppie" suburbs (I'm kind of quoting Chris Potholm there).

In these races the vote of Maine party members (or Independents who enroll in a party the day of the primary) will actually matter, whereas the presidential nomination contests may be effectively over by the time of Maine's Democratic caucus at least (and it may be difficult for a candidate to claim victory in the Maine Republican caucus until the state convention which will be held long after the Republican nominee is clear). I doubt Maine's vote will make a real difference in November either, as we're more Democratic than the nation as a whole, plus it would be unlikely for no candidate to win 270 electoral votes not counting Maine's 4 (although it came fairly close to happening in 2000). There can still be presidential coattails, or course, but I'm mostly focused on congressional and more local races as far as Maine is concerned.