Allowing you to see your previous load out for a song that's replayed, and/or allowing you to see the individual scores for each load out type you've used on the song. Perhaps this is something that can be coded into FB and bought with coins?
Reason: I'm lazy and don't feel like creating my own spreadsheet when trying for high scores. :p
Edit = Doh, I just noticed a few pages back that Doc mentioned this. So, I concur.
1) For the Facebook app and spending coins, create some sort of step-ladder tournament that you can "buy-in" to compete. You can utilize the Score War mechanic for each round (that way, you can allow the players to each choose a song that both has).
2) In the same vein as #1, create leagues like Euro football. Based on skill, you have groups of 20 players that Score War for a month, with 5-10 divisions (or however many people join). Depending on record, at the end of the month, Top 3/Bottom 3 are promoted/relegated to the adjoining leagues. This could also have a buy-in, and perhaps at the end of the month the champions of the respective leagues get a Title or something cosmetic for their FB name.
As long as there's a competitive aspect to this game, we might as well explore and promote it, right?