We should have two days for Walla Walla
 

Although I live in Oregon, haven't been to Walla Walla since I was a small child.

Other than wineries, what should I add to my list for a short trip there?

This website should be helpful. http://www.wallawallawine.com/#events-home
I had no idea that there were that many in the area.
The only one I know anything about is Doubleback which is owned by former quarterback Drew Bledsoe. Drew built a beautiful home in Bend Oregon.
There is a beautiful park in Spokane if you want to go that far.

Actually, there's a surprising number of things to do in Walla Walla.

The Fort Walla Walla museum is unexpectedly good and well worth a visit. You may have been to some wineries before, but they have increased ten-fold in the past few years and some are very good with lots of tasting tours available. The Creek Town Restaurant is one of the best restaurants I've been to in ALL of Washington State, but it has a bad habit of closing down, so check if it's open. If not, the Marc inside the Whitman Hotel is pretty good (and the hotel a good place to stay). Outside of Walla Walla along highway 12 is the Whitman Mission Historical Monument documenting fascinating history of the area. A stroll around the Victorian neighborhoods surrounding Whitman College takes you by some really nice 19th century mansions and there are nice drives through the rolling Palouse country, or up into the Blue Mountains out of Walla Walla.

When would you be traveling?

Late May for travel.
Restaurants sound neat.
As a child I read a lot about Narcissa Whitman, so the Whitman Mission might intrigue me.
Strolling around the Victorian neighborhoods might be fun too.
Tomfuller, lots of beautiful (high priced) homes in Bend; didn't know about Bledsoe.

I looked through the list of wineries and am not familiar with most of them.

Speaking of Victorian houses--did you locals know that some of the best-preserved are in the little out of the way town of Union, OR?