To work around the 1000 songs thing: tap the Browse tab, browse to folder with songs that weren't included. Wait a second, then go back to Artist/Albums/Songs, they will be there and the app will know about them unless you sign out (which makes it forget everything).
The limit is based on what the Dropbox API can return, but Tunebox itself is designed to be able to index a lot of music.
My wishlist: I would like to download some albums for offline use and I would like to have the app index more than 1000 songs.
But don't take these suggestions as criticism. I love your app and it is already extremely useful!
Great work!