I think it's best to wait a bit. Stabalize the ownership situation of the teams having some trouble right now.
We've seen how rock-solid hockey markets can be hurt by unstable/bad ownership. Boston, Chicago, Pittsburgh: they weren't drawing nearly what they are today when they each had ownership issues.
I'm not going into the problems of Phoenix and the Isles.
Firstly: I'm not a local and/or don't follow them closely enough to know the deeper reasons behind their troubles. Articles, blogs, message boards are good for basic info; but that is usually slanted and doesn't always get to the heart of the story.
Secondly; the troubles of these two have been beaten to death around here.
I lived in Nashville when they were having their issues, so I heard a lot more at the time. And now that they seem more stable, I don't doubt they will continue to grow in that city. Really don't like the Preds, but there are a ton of fans there for a mid-sized city.
For Atlanta, I've lived it for the life of the franchise. Hard to grow at all when ownership doesn't give a damn about the team, and does little or nothing to market them. They have no footprint in the city, no identity in the local sports culture. It's hard enough to compete for entertainment dollars of three other major sports franchises (as well as the king here; college football), but it's impossible when the owners do nothing to even try to attract fans.
Many say this is a failed experiment. I'll say the experiment hasn't started; that's how epically bad the owners have failed in the last 12 years.
--Make the fans feel like they are wanted/welcome, more will come. It's too entertaining of a live sport, and seemingly half the city comes from somewhere up north.
--Ice a good team every now and then, more will come. Every city has it's bandwagon fans, but Atlanta always seems to have a few more. Harsh, but true. Won't hurt me (or the team) if those people start showing up.
32 teams are doable, just not right now. Give it five years or so. Let these situations stabalize. The talent pool should have increased (not that it's diluted now, but I know that some are stuck on that opinion).