Regarding "jack[ing] up your FID count", you could have the same tune on your player 10 times, and there would just be 10 entries in the database pointing to 1 FID (music file on the disk). I think you're confusing the number of FIDS with database entries, and the two are independent of each other (unless you have only one database entry per FID, and then they are roughly linear.)

That said, you can run into problems if your database gets too large, but it'd have to be pretty huge. I'd say go ahead and make your mood playlists. If you run into trouble, you can always remove them.

EDIT: Oh...right...I forgot that each playlist gets a FID too. Still, not too much to worry about...