As a bard, I tend to use my songs as a "oh shit, someone is almost out of resources" button over using foe. If the healer is < 50% mp, time to help out the healer. If I'm almost out of TP, I make the assumption that some of the other TP using classes are probably at least getting low, so it's time to use peon.

Having the magic classes deal more damage is great and all, but if I don't have the mana available to keep up the other two songs when needed, it's a larger problem. Healer runs out of mana? People are going to start dying. Classes run out of TP? Their dps plummets.