If I'm changing my avatar, most likely my signature will change to match it. The same would apply if I'm changing my signature, then I'd find or make my own avatar to go with it. Normally, I'd go with an icon-sized avatar since larger avatars, while nice, don't always look good either my username (or maybe that's just me, idk). I have a tendancy to change my post theme a lot though - with the exception of my current theme, because it's so me. n__n; Still, I'm in the process of changing it soon.
I used to change my profile colors often, but gradually the duration of the time I kept it would continue to last longer and longer. I recently got tired of the current profile set up I had, so I removed it in hopes of putting something different [and simple] up. Unfortunately, I'm in little rut where my creativity is a bit on empty. I'll get to it in time though.