We've never had Avatars. At one point, the staff put up a poll to let users choose between Avatars or Signatures. The members overwhelmingly chose Signatures. MacNN forums focus more on content, that is why sigs have the size limits. I've visited other team forums with no limits, allowing avatars & sigs, and I have to agree with the limits. In many cases, the avatars/sigs are bigger than the actual posts.
The low-contrast icons are a pet complaint of mine. Among other things, they aren't hard to tell apart for the colorblind -- they look identical for many such people. Use the Universal Access Pref Pane to remove color, and you'll see.
The proper place to complain about it, or to offer an alternative icon set, is
this thread in the Feedback forum. I've offered both. The more people who do, the more likely it will get fixed. Note that the designer is currently stuck without internet in Germany for a few more weeks, so this is an excellent time to rack up complaints, or build support for a particular set of alternative icons.