I had all three of mine eventually master songstress just so I could get a kick out of hearing them sing--- especially when Paine would say "I hate this dressphere" before executing the command. But I do think all the other ones are worthwhile.
I actually end up using the Lady Luck sphere a lot, too-- granted the attacks aren't the most powerful, but I've seen weaker ones with other dresspheres-- but the double EXP is awesome for leveling your characters up for later chapters, especially if you wanna go to Bevelle in Chapter 5. Anyway, what was I saying? Oh yeah, I think they pretty much all have some bonus, the attacks are pretty cool and some are even funny. It's worth it. :moggie: