For starters, you should define what a Large Art Constitutes.. dimensions wise. Same would go for Signatures. So people can place there work in the proper sections.
Some of the sections seem unnecessary, imo.
I would get rid of Avatar Showcase. Avatars are usually 100x100 or a tiny bit bigger artwork. Nothing too special to gawk over. I see there is a thread currently in there. Looks like the OP created it larger anyways first. It could easily be moved to another section.
I would also do away with "Tagwalls" as these can easily be placed within the "Large Art" section.
I would do away with Photo Manipulation. All images that were to be placed in there could easily be put into another section.
Portfolio section seems to be a waste as well. What I would do is.. create an option for a person to add a portfolio link in there profile. Then make it so when people look through the memberlist.. the portfolio button is visible on there as well.
Also.. in the "Featured" various art threads. You should hide your signature
Breaks up the flow of the images. (of course imo).
That is all Ive got for now I suppose.
Cheers
Syn