[DinkumThinkum]

Increasing the two attributes the Bard's Music skill depends on would probably help, but I don't think any of the expert skills has a specific benefit for a Bard.

As far as I know, Power Cast only applies when characters actually cast spells themselves; it doesn't affect casting spells with scrolls, bombs, instruments, gadgets, etc., so it's useless for non-casters.

Most of the other expert skills have at least a limited application for any character.

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Dexterity of 100 gives Reflextion, which helps armor class.

Senses of 100 gives Eagle Eye, which helps with ranged weapons.

But I can't think of any that would specifically help a Bard as a musician, rather than just helping their offense or defense.