As far as performance goes, you can get some easy improvements by making some upgrades. The site currently runs php 4.4.4, but php5.x enjoys many performance (and security) improvements. Same with moving from MySQL 4.1 to MySQL 5. Also you get the new version of Zend Optimizer (if you want to continue using it) with php5. Also applies to Apache (site is running 1.3.37, 2.2.x is much improved).
Don't run sshd on port 22 unless you enjoy little Chinese computer hackers banging away on your server.
In the gallery, you should give uploaded files unique names rather than using the name provided by the user. People using something like 4.jpg are going to overwrite eachother. It makes more sense to use the photo id # from the database as the filename (plus extension) as that will always be unique.
Making the RSS features of vBulletin more obvious might be appreciated by some members.
I personally think
SMF is a better forum system (especially in terms of performance, and can convert databases) but I imagine you are already vested in vBulletin and all the plugins you have with it.