I'm thinking of starting an account on Etsy to sell my artwork...any thoughts/tips/warnings/kneejerk reactions?

I think you should go for it. I don't know how Etsy works though.

One concern I have is -- do I devalue my work by putting it there (or anywhere online)?

hmmm. Interesting question. I don't think the idea of putting it online will inherently devalue it. Where you choose to put it could.

I think of etsy as a more crafty place (but that's my view of their brand). There's art.sy that's a bit more highbrow.

I get the same impression from Etsy, though obviously people sell paintings there too. I took a look at Art.sy, doesn't look like you can sell stuff there though. Different URL?

Wow, there is a lot of *awful* stuff on Etsy...