Just following up on this. I enrolled in the Port Valet program before the trip. Flew Delta. Didn't need an account unless I thought this would be a recurring thing in Seattle, so just enrolled as a guest. Enter your flight and cruise info and they take care of everything, for free (it's a smart idea for the city -- gets us out there spending money). The day before, information and our bag tags were delivered to our room. We just put our luggage outside of our room the night before and they were at baggage claim when we arrived at our home airport. You can also check on the status of your bags.
Also want to recommend this city tour from Tours Northwest: https://www.toursnorthwest.com/tours/seattle-city-tour/
or https://www.viator.com/tours/Seattle/Premier-3-Hour-Seattle-City-Tour/d704-5396P10
Sad to say I was disappointed with Seattle. Before the cruise we stayed downtown at the Westin and while I'm sure the city was once beautiful, it felt (holding back on the colorful adjective I really want to use...) sketchy and unsafe, unfortunately, especially after dark. The tour was great because we got to see highlights of Seattle with a fun and informative guide (Bryan). Otherwise we would've just wandered around aimlessly downtown.
After disembarking went to Pike Place market. Not much to do on a Sunday morning at 8:30... things are just opening and if you're not hungry there isn't much reason to go -- except to say you did -- and snap some photos. Also went to the museum of pop culture, which I can recommend if you're a music fan of a certain age : ) From the pier/pike place area, I would suggest walking to 5th and Pine to Westlake Center Station at 400 Pine Street and take the monorail right to Seattle Center (where the museum, the Space Needle, and the glass museum are). We took a bus there and the monorail back; the bus was much less convenient. Buy your monorail tickets with your phone and skip the kiosk line.