AAC is not well supported yet, and our metadata parser for it has some issues. That's probably all of that, for now. When the support gets better, tagcache will read it better.
There's no NOT or OR operator. There's plans for them though.
It looks like you've got the rest of 'em right. They're not actually documented yet because they may change before it's "done".
As for your question about "levels" they aren't really levels. You just have cascading filters. One of them just has one filter, the second has several filters, which should decrease the results as you go down more levels. Basically, it shows results, and then you can see subfiltered results.
I _think_ the last thing you're describing is a known bug. If you filtered by the year 1985, and an artist had ONE song in 1985, for some reason when you picked that artist you'd see all songs by them. That's a bug in TagCache for the moment.
If I misunderstood something, let me know, and I'll attempt to clarify.