I always look at bards like one does an author in now a days..
In my mind a writer and author is someone who is in it not to make money, cause you can't really make money writing. (There are exceptions but anyone in the industry will tell you that making money writing is HARD!) They are in it because there is a view of the world they want people to see. They want to entertain, they want to make someone sit back and think.. or they even want to rile people up and make them scream with rage!
It all depends on what gets you going as a crafter of a written art. Same thing for visual media really or instrumental.
You do it because you enjoy watching what others think of it, for good or for ill. That is why you show it to the world. I think honestly, it's kinda a bit cheap that magic/prayers/singing all have the same results in the game. That means that in an wider lense there is no difference between what a good bard can do and a good cleric can do. There is no diversity if we can all fly, heal , ect ect ect. But that's the way it is, rules wise.
In a role playing perspective, I think every bard character should have a goal. A passion, an explaination to why they want to show THIS that they made tot he world. And that is what sets that character apart from a fighter or a thief or a cleric.
Are they in it for the glory of seeing their name in print?
Are they doing it for their family their people so they are not forgotten?
Are they doing it for money?
Are they doing it because they are dying and want to be remembered?
Are they doing it for the joy?
Are they doing it for a loss they have witnessed or happend to them?
Are they doing it to rile up the masses?
Are they donig it to make sure people know that good is bad?
Are they doing it to honor a god or goddess?
This is, to me, the BIGGEST factor in a bard. Why do you want to do publish, why do you want to create. What is driving YOU to this goal. And it's even more important to me than actually being published. Being published shouldn't be somethign that is just passed over as being common place. It's a big deal to get to that pinacle. A good part of role playing a bard to me, should be the struggle to get your act together and decide what you are putting out in the world and why... And then having that struggle both internally and externally to get your dreams in line.
Being a bard to me, is a lot of chances, a lot of making enemies and then friends and then enemies, because your goals are generally self serving. YOU have to do this story because of THIS reason. It's always very personal drive. Which is why bards are so independently motivated and seem to have limitless energy. For they cannot afford to sleep a moment and let someone else take their lime light away....
But that's just me.
What was my point?
Oh the biggest thing that makes a bard a bard is the reasons why they need to have their craft out there. Drive. Passion. These are the things that make them more than just a simple cleric or magic user. Or even mroe than a thief. For even the most humble of Odgma's scribes that is bard has to have a reason for hugging scrolls.