I don't think we need a two tier system and I don't think we need a rating system. I have textures up here that have been downloaded over 2,000 times (or at least looked at that often) I have had people tell me how good they are and how they appreciate them but they haven't rated them. I don't mind that because I do not normally rate things either. And I think a lot of people don't really want to rate things here or at other sites. force ratings and you may get a lot of ones and not much else
What the site does need is a team of people who are knowledgeable enough to know when something is a copyright problem and a system to stop cheats.
If you only use the number of downloads how does that help with some of the items that are not for downloading. Maybe a daily limit per person on uploading might be an idea because then people might put more than one texture in a download.
Taking things down if they haven't been downloaded for 90 days is not a good idea either - unless the site is short of space and no-one has said that is the problem. I know that quite often I will browse for some thing for a model that is really old and probably not very popular but just for one image I need it and again I am sure there are many like me.