Haphesto said:
What would a bard bring to the group if the group already had a mage+enchanter+shaman, then? Those are pretty common classes due to their usefulness.
That's why stacking is important.
It's true that stacking is one way to make the Bard class more useful and sought after in groups and raids. And it makes sense to me to have both spells and songs in their own line. On the other hand, I can see how having + 40% to spell damage would be really really overpowering. One way to get around this would be to nerf both of the lines, so that together they have a max + 30% song damage (10 to bl, 20 to relic song, or whatever). (For the record, after some thought, I've decided I'm against this idea).
On the other hand, Bards have classically been a mix of many classes. We're OK enchanters, and OK rogues, and OK DPS. The advantage to a bard in a group is utility: you can lose a shaman/enc and not worry because you still have haste and slow and CC. We aren't as good as any of these classes, but the utility makes up for it: bards are great in groups.
Unfortunately when you get in a raid situation, you never don't have an enchanter or shaman on hand. And rarely do you not have a beastlord (unless you're Legacy

) Now, because of stacking issues, bards' utility is significantly reduced. Even so, there are a few reasons to have a bard:
1) Resists. PoT4 and elemental/purifying chorus stack with all other resist spells. Resists are very often crucial to a raid's success.
2) Song haste. Although not all bards haste songs classify as "song haste" we do have some 30% song haste that will stack with spell haste.
That's pretty much it. So, assuming your raid force has at least one enchanter, one shaman, and a beastlord, two bards work fairly well on raids. If you don't need resists, then just one will do.
Additional thoughts:
HP/Mana regen: I know everybody is gonna say that this is the best part about bards. While it is true that bard's HP/mana regen song exceeds the mana regen component of JB (thank goodness they stack), most players forget that in-combat mana regen is hard capped; In other words, past a certain amount of regen, nothing takes effect. Between JB (which, as a buff, doesn't take up another potential buff slot (like it does with bards), natural meditation regen, and FT items, there is really very little utility for Mana regen during combat. While it may be nice out of combat to speed up the down time, it's not at all necessary, and besides, the one bard that's playing the resists/haste can sing it, if need be.
Spell line song haste: Adds some useful stats, even if the haste portion doesn't stack. Then again, if you're really high up there, you're stats are maxed anyhow and it becomes purely useless. Additionally, this line of songs is group only, not AE.
DoT damage/melee damage: Fair, tbh. Then again, you could replace us with a rogue or a necro and do much much better.
Well, I hope this has been informative. Let me know if I left anything out!