Finally, as a side note, if these special abilities are designed to have "an imperceptible impact on game balance while remaining thematically consistent to the flavor of each character class," then why bother to bring them up?
Lots of stuff has no impact on game balance, but adds flavor. Your character's hair color, height, gender, regional background, family ties, raging dislike of goblinoids who burned down his whole village, etc, etc. Sure, you could name all of your characters 'Bob the Fighter' or 'Bob the Wizard' and not bother with all that silly non-combat stuff like characterization or role-playing, but I think you'd be remiss to forbid the rest of us the chance to play our little games the way we like to, with characters that have names and families and appearances, sometimes even lovingly drawn pictures from those with artistic talent. Sure, there's no mechanical benefit to having a picture of your character, or knowing that he has an antagonistic relationship with his step-father, but some of us enjoy creating stuff, and just because *you* don't care for creative little details that don't add to your kill rate, doesn't mean that the rest of us can't enjoy more of the game than how fast the character can burn down every Orc in the room.
A Duskblade learning his trade from the elves, and picking up tips of elven etiquette during these interactions with his ageless mentor is flavorful, and not terribly important to the game. But it's *flavorful.*
If you don't want anything in the game that doesn't have a noticeable mechanical benefit, role-playing games might not be your ideal hobby. You've made it clear that you don't see any reason to introduce anything to the game that doesn't directly benefit your character and make him noticibly mechanically better in a fight. That's cool. Sometimes I like power-gaming too, and I've played with plenty of people who'se idea of 'role-playing' is to whip up a Spiked-Chain-wielding Goliath named 'Bob' and go to town. It's a big hobby, there's room for that, but I don't think that's *all* that D&D is allowed to be.
I think that there is *also* room for stuff that isn't mechanically crunchy and geared around letting your Bard kill Orcs faster than ever before, but in fact simply makes him a little bit better at being a Bard.