I totally agree. Everyone's got bard nailed as a crippled subjob, but I think that's mostly because all the FAQs and guides out there just copy each other without trying anything themselves.
What you LOSE by playing bard as a subjob is exactly what you lose by playing any other class as a subjob... you're effectively at 1/4 of your potential power... you are at 1/2 your main job's level, and you can only put one song on a given target, as opposed to two.
As any mage class, you're at 1/2 your main job's level, and you've got half as much mana as you would have at your already halved level (so a level 30brd/whm will have HALF the mana of a level 15 whm).
Since bards don't deal in mana, I think it actually makes a splendid "magic" subjob for any already mana-less main job (whereas mana'd subjobs suffer more because of the tiny amount of mana they receive as a subjob). I'm playing bard/thief right now, and I'm planning on playing thief/bard once my bard catches up to my thief in levels. How many thieves do you know who can cast a party regen spell?
For Beastmaster, yes I think bard could make a good sub, if only for the charisma bonus. Bard is definitely party-oriented, and the songs aren't effective enough to boost your solo power as much as, say, a rdm's curative magics + en<element> magics might. But you won't have to worry about mana, and that charisma bonus will come in handy. And if you do actually play in a lot of parties, then more power to you!