Portland to Corvallis includes most of the interesting stuff in the Willamette Valley-- that's a lot of space.
We've eaten at the Sunnyside Up Cafe in Corvallis a couple of times. It was pretty decent: http://sunnyside-up-cafe.com
If you want to go to Silverton, there's a cute Asian stuff store and some good antique/junk stores (and a good Thai place), and a number of good coffee shops. It's a little ways off the I-5 corridor but nice if you want to walk around a little.
Salem doesn't have much, unfortunately. You'd think the capitol of the state would have some sort of culture going on, but unless you're really into big box stores it's not worth visiting. (There's a good Children's Museum, but I seem to recall that not particularly relevant for you. If for some reason you are hauling around kids, it's worth a couple of hours to run them around a little.) McMenamin's is a decent sort of pub restaurant if you want beers and veggie burgers that you have to make sure you specify should be vegan. We usually end up eating there once or twice when we're in Oregon just because they're at least consistent (that one veggie burger they have on the menu is usually okay and they make good fries) and the beer is good.
Wave at the exit for Stayton as you motor by on I-5, but don't bother going there. Not even a good coffee shop, and people there have managed to open a number of good restaurants over the past few years, all of which have failed utterly after not very long. That's extra unfortunate since I grew up there and my parents live there and it's pretty hard to find good food when we're visiting, at least without driving an hour or more north or south.