Noting that you're in Washington, there are a lot of roads out there into the mountains where you won't be "legal" without snow tires (you need the snowflake symbol on them, all seasons don't count).
Don't know the roads you use, but I-90 for example might cost ya if you get stuck in traffic when the "chain law" is in effect AFAIK
The forum (BST) might even score ya some stock alloys in 15" cheaper than new steelies, so keep an eye out (junk yards as well).
Even cheap snows are like driving on wet pavement in the snow compared to slithering around on those 17's.
I tried it on tires that size last year a couple times, and though it worked on the flat i had to be REAL careful how & where I drove with them.