Hm, well, Proboards is pretty much the "lowest common denominator" of free bulletin-boards (in other words, it has bad signalling value). Most of the time when people see a Proboards message board, they'll think that the board is most likely a low-quality board. Because most Proboards forums are low-quality (even though theoretically, there could be high-quality ones - although the high-quality ones almost always end up switching to an independently hosted server or vBulletin. Not that it's necessarily a good thing - I'm surprised why there seem to be no good discussion boards centered around Proboards)

Given the lack of activity on the proboards forum, I don't think a switch to vBulletin would confuse all that many people. And it would probably look better.