The vB support is MUCH better than IPB. When I forked over the 85 bucks, I really got what I paid for so to speak
As for mods, 3.0.0 mods work for 3.0.3 for the most part, you might have to change some coding around, but if you ask around you can get answers fairly quick. As for 2.x.x mods, I'm not too sure about that one. It was a different software alltogether.
As for skinning, I find vB MUCH easier to skin than IPB...and the code is a lot easier as well. I'm currently writing a more server friendly version of the Affiliate mod as we speak. I don't know if I will release it just because my needs might not be up to par with others, beings the other affiliate mods here are FAR more powerful...but overall with vB coding vs IPB coding, it's MUCH easier.
Oh, might I mention, if you get vB, they have Impex. A nice little tool to convert your current IPB database to vB, so you won't lose anything...other than a few hours making sure that everything is squared away. It's really nice though, and I recommend it.