I have a character in a game nick named "captain cleric" who uses a "power up dance" of bull's strength, endurance, and eagle splendor. I do not use metamagic to accomplish this, but I have never been pushed pasted the duration of the spell. It lets me become the fighter. When the party has a fighter, I usually can't do as well, so I go more towards summoning. At 9th level, the pre-casts still makes the Captain nasty, and probably a bit less fun for the others.
I play a 16th level incantantrix though that used instant metamagic and the fiendform spell from FR to be an imp all day. I now know that this doesn't work, but it didn't really matter. The barbarian carved through most of the combats any way.
My point is that persistent wouldn't or didn't make too much of a difference in either case. There are other ways to stop running spells. Try look at the "spell engine" spell in magic of FR. Walk into lair, get all your precast downed, and trigger an alarm.
I play a 16th level incantantrix though that used instant metamagic and the fiendform spell from FR to be an imp all day. I now know that this doesn't work, but it didn't really matter. The barbarian carved through most of the combats any way.
My point is that persistent wouldn't or didn't make too much of a difference in either case. There are other ways to stop running spells. Try look at the "spell engine" spell in magic of FR. Walk into lair, get all your precast downed, and trigger an alarm.