Well, it's been mentioned a thousand times by a hundred different people I'm sure, but really dude, you should offer the ability to download all the current tracks at the same time, for like 10 to 15 bucks. Many other similar sites offer it...
You could also add extras, such as uncompressed versions, loopables (though I think you already offer those for every track, very impressive!) stingers, or even occasional extra tracks, but nothing says you have to do that if you want to keep it totally fare... After all it's your site.
You could make some extra money for running the server that way, I'm sure your costs are quite high, and you can always limit the full package's download speed to like 700KBPS (something reasonable) as to not overload it and impact other visitors.
Otherwise people are just going to use a mass downloader like "winget" or something anyway, which will have a much bigger impact on your server.
Just have them enter their email optionally so they get direct download links to new tracks when they come out, to add to their current collection, or even offer a URL in the package that goes to a buyers only page or smaller package that will easily update their collection.
You could also include a license in their that will work for all the tracks, which is easier than finding it on the site and can be shared with no effort in TXT form.
You make some awesome stuff, and I will donate when possible anyway, but seriously sorting through it all takes a lot of time and their is always that sneaking worry that your site will go down some day and this amazing resource will be lost!
This... -- Is CNN'.
Well Ted, it sure looks like there's been uh, quite a bit of violence around here
"aaoh, that violence was terrible'!"
Yeah it was, pretty bad.