There is -never- a good reason to be sober as a bard.

As someone who perfected all the songs, I will say I
didn't notice if being drunk itself acted as boost to
to learning, say in the way a Tome of Knowledge does...
but I know it helps because you gain more mana back a tick
when you are drunk. It's the reletive equivelant to being
slowed, well not quite that nice, but better than being
sober, none-the-less.

Just my $.02

Nery