I don't see why there should be any 'privileges' for posting, lol, considering you're coming on here to post and have a good time anyway. You post well enough, you get emblems. I don't see any real reason to add anything else to this simple system.
Edit: on a side note, something I'd change would be to make the default avatar size 160 x 160px, simply because that's the same size as some of the photosets on Tumblr, lol. I know it wouldn't ever happen, but it's a nice thing to think about regardless.
- GLaDOS (Portal, 2007)