Maybe instead of outright categories, use del.icio.us style tags? That way things can be in multiple categories, you can search by name, user, tags, date, popularity, etc, you can see all the requests with certain tags (select multiple tags to narrow it down) and so on. When people go to put in their tags, have it suggest already made tags in a dropdown or something in order of popularity as they’re typing them so they’re more likely to pick one with a consistent spelling. On the main page you could list popular ones, recent ones, random ones, or whatever.
Using tags would be more flexible than categories IMO. For example, what if I didn’t like the interface for a modeling script and maybe didn’t think the script itself worked very good? Would I file suggestions under UI, Modeling, or Scripting (you didnt list a category for python…)? With tags I can put it in all 3.
Of course this opens up the problem of people spamming things on all tags but I think if you make it so people have to register an account and then the suggestion shows their username it would cut down on that. If so-and-so spams something on all tags… mark it as spam, delete it automatically after n number of days and no one would take them seriously next time (maybe put a red dot next to their name or something to show they’re been reported and flagged recently)