I have to agree with you one that one.
But for skins and wallpapers we are talking about 2 different beasts. We do not moderate skins for quality, only wallpapers. The only reason we reject skins are for copyright reasons, for the most part (as well as other ethic reasons such as pornography or such). Wallpapers on the other hand, we moderate, as you know.
So, if indeed we agree that a lot of skins are starting to look alike, we won't do much about it, other than hoping that some talented skinners start getting a bit more originality. Also, there is the "popularity syndrome". Some people are only after the download numbers, and I can tell you that often, the most popular skins are the least original ones. A lot of people have very conservative tastes.
As for wallpapers, we have actually started talking about it. Indeed we found that a lot of wallpapers are starting to look alike. There seems to be an increasing number of people making 3D abstract kindof wallpapers. Although we have nothing against these, when it startes being pretty much the only thing that gets submitted, something needs to be done. So, we may start being even more picky on the wallpapers and the Bryce stuff may even more than before start to be rejected. Not because they are not nice, but because we want a bit more diversity. But again, it's very informal yet, nothing has been officially decided.