Why don't Republicans make more of a play for Maine?

[Sol]

It's unlikely that the GOP will nominate a presidential candidate moderate enough to win Maine in the near future.

What if that candidate campaigns on economic issues and downplays the social issues?

You are aware that a significant section of Maine's voting base is closely tied to unions, right? Particularly in ME-2, which has a lot of old industrial towns like Lewiston/Auburn. Emphasizing economic issues is a recipe for disaster in Maine too.

[Sol]

Because it's unwinnable for them, like the rest of New England.

What about New Hampshire?  That's winnable for them.  Most people there get Boston TV stations, and I'm sure they share much of that audience with Maine as well.  Making ad buys in the rest of Maine (and New Hampshire, for that matter) would probably be pretty cheap.  (Of course, they would have to downplay their social conservatism as well.)  Maine may lean D, but I don't think it's out of reach for the GOP by any means.

I don't actually think Maine gets Boston stations. Anyway, Southern Maine is not GOP-friendly.