Aside for the PhpBB, these forums already have everything you suggested. I guess you just haven't really looked. Really not at all because it is all easy to find.
PHOTO GALLERY: [link=http://www.spawnpoint.com/asp/Gallery.asp]http://www.spawnpoint.com/asp/Gallery.asp[/link]
GENERAL CHAT: [link=http://www.spawnpoint.com/asp/tt.asp?forumid=23]http://www.spawnpoint.com/asp/tt.asp?forumid=23[/link]
RANT ZONE: [link=http://www.spawnpoint.com/asp/tt.asp?forumid=52]http://www.spawnpoint.com/asp/tt.asp?forumid=52[/link]
And really alot of the sections can be used for general chat or humor, they just aren't specific to it. And if you hadn't noticed, there already have been a number of threads involving general humor and chat. You just haven't explored very much I suppose. Check in the Ancient Admin forums every so often. They are always good for a laugh. As for PhpBB, without using it Spawnpoint is doing two things. They are refusing to conform to the aristocratical rule of PhpBB, and instead choose to do things their own way.
They are also capable of doing more with the forums by not using PhpBB. They are not restricted by the template of PhpBB. They can play around a little more. But feel free to make suggestions still because they are always looking for more ideas to improve the site. The forum skin ideais good.