I think it would sell well if it had Cameron's name on it, other than that, I don't think it's a good match. Not just Starcraft, but Blizzard games in general are well recieved, not just because they look good, but because they're great games over all. The story is good, the gameplay is good, Blizz works on the game to make it better after they release it, more than just making sure the glitches are ironed out.
Looking back through James Cameron's IMDB page, he's done a lot, and a lot of it is CG/SFX driven. I think more to his credit for a Starcraft movie would be stuff like Terminator and Aliens, Zerg kinda look like Aliens. Avatar looked awesome, but kinda lacked everywhere else. It was still good, I just don't think it lived up to the hype machine. Titanic I put into the same boat as Pearl Harbor (the Ben Affleck one). Disaster movie that had nothing to do with the disaster it was named after. Replace Titanic! with any boat that sunk, same story. Replace Pearl Harbor! with any city that got bombed in any war, same story. When the PR machine rolls, every one wants to see what the hype is about.