Frankly, I think the problems with the forum performance have more to do with shitty programming than anything. It's not just that they've hacked the shit out of the vBulletin software they run, it's that they haven't even done a very good job of doing so. Combine that with some seriously shitty, outdated server hardware, and you've got a recipe for exactly the constant problems that site has.
There's plenty of other sites out there of similar or greater traffic levels that use vBulletin without realy incident. Gametab and EvilAvatar for example, both run vBulletin software, and get a pretty heavy amount of traffic, and by and large only Gametab has ever given me trouble, and that's just the occasional "sever is too busy" message, somewhat understandable given that it's the single most popular gaming news aggregator on the Internet.
Basically, if their servers weren't shit, and their software weren't completely fucked up, Tangency wouldn't really be a problem at all, and at present state, even if you completely deleted Tangency and all it's contained posts, you'd still be running into constant problems because of those two factors.