Actually, if it meant I could do more DPS during the times where songs aren't needed, I'd gladly give up "Party-wide" buffs in an instant.
I've said it before and I guess I have to say it again, "party-wide" means nothing. Your melee/tanks will not need MP. Your casters won't either if they're played right. Your healers might, although less likely if people don't keep dying and draining MP on revives.
So let's say I'm doing a 4-person dungeon with a warrior, white mage, dragoon, and bard. In that case, what does it matter if my ballad affects 4 people or 1?
Let's say I'm in a raid with a WAR, PLD, WHM, SCH, BRD, MNK, BLM, and DRG. Why does it matter if my song affects the entire party if only 2 people are even possibly going to benefit from it and the other 6 won't?