I think he'd be a great fit in Portland for a number of reasons, but I want to address a few of the supposed "problems" of Nash in Portland...
1) we play at a slow pace...
This is partially true, however we've picked up the pace considerably since Blake has been out (showing part of the problem) and have the tools to run the break adequately well (at least average). Nate also always talks about getting out in transition more too (at least in timeouts) and I think he'd trust Nash to get out on the break a little bit (because I believe he's pushing Blake to. So I guess while true, I think our pace would pick up if Nash was here.
2) Nash can't run a half-court team and won't succeed in the playoffs.
Again I don't think that's true, while he does like to run (and is damn good at it) I don't think he pushes too much, and he can play very well still in a slowed down game. This guy's been to the WCF multiple times, had ice in his veins playing in Dallas (remember our series with them). He can run a team in the half-court, and I think he'd really accelerate the growth of LMA and Oden because he knows how to get people the ball in the post (and our cutters would benefit a ton too).
3) Nash would not work well with Roy
I think this is simply a load of crap. As I've said many times, Roy does need to grow off the ball, but he's played off quite a bit before and lately (with Blake out) Roy's been cutting to the hoop more. Roy has skills in the post (remember his rookie year) and can get out in transition well, but he's responsible for so much of our scoring and creating load that he doesn't have anything left to do that anymore. While Roy should still be the guy isoing at the end of the game and be our main scoring option Nash is a good enough shooter to adequately space the floor (ala Blake) and would be much better at spreading the ball around than Blake. It would make Brandon's job easier and he would still be the star (even though his assist numbers might go down). Remember D-Wade, Lebron, and Jordan all started out as the primary ball-handler on their team and later benefitted by their team's playing them next to a PG instead of another SG or SF.
4) Nash is too bad at defense to help at all
His defense isn't great, but he plays well in the crunch and is intense and persistent. In addition, an LMA-Oden-Pryz three headed monster is pretty good now and very soon will be better than anything Nash has ever played in front of (on D). We'd need to go a little more zone perhaps, but Blake sucks at D too. What we'd gain in offense would more than make up for the miniscule loss in defense.
5) We don't need another "star"
A star that makes all our other players much better and speeds up their development while taking few shots...please
6) Nash would want to be "the man"
I think Nash (at this point) would be fine going 25 minutes a night. He could play a less strenuous load here, it's close to Vancouver, and we could still develop Roy, Fernandez, Rudy.