The few level spells that I use are already 9999 damage worthy, so no worries there:
Update:
Continueing through Kefka's Tower, most bosses are really easy. The Dragons left to kill were done in a hurry. Oh, hurray, got Crusader, even though I'm not gonna use him.
Then coming to the big bossas:
Celes vs. Guardian: The fight took longer than expected, which made it feel challenging. ^-^
Setzer vs. Doom: Just going mad with Ultima.
(crappy pictures, but meh, I felt like taking them :P )
Edgar vs. Goddess: Realized that some of the Tools do 9999 damage. ^-^
Now, Celes vs. Poltergeist: that s.o.b. casted Stop and then some sort of ball damage that does instant death. -_-
meh.
But, it advances surprisingly well. I can't wait to (well, kick Poltergeist's ass) go further on to the 'tier tree', or whatever it was actually called. =)