Will it notify me per email when a wishlist game is on sale like steam does?

No.
Edit: I guess it's only use is to keep track of what you are interested in.

It scratches your belly when you behave right.

No, but you /can/ sign up to get emails from GOG notifying you about weekend sales, and if you then go to the sale page, any games you'd wishlisted will have a little heart icon next to them.

fixed

Khmm . You forgot about Carmageddon .

Ask not what the whishlist can do for you - ask what you can do for the whishlist.

If you look at your wishlist when a sale is on you can see which ones are on sale, besides that since no one can see the list.....ya

In a thread I had long ago, a staff member confirmed that they do indeed look at the wishlist to see what games the users want, so it's a valuable way for the users to communicate which games they would be interested to see here. :)

EDIT:
I'll leave my reply, but I just realized that you were probably talking about your personal wishlist, not the community wishlist.

Some folks share theirs on the GOG wiki site. And with the next version of GOG (which they're working on), you'll likely see more wishlist features (like sharing and email notifications).

And maybe one day it will be no more wooden, but a real boy.