I would strongly recommend getting the Seattle CityPass. It costs $100 and you can see five attractions with it. Most of these attractions are walkable or a short drive from each other.
I got Citypass in January and went up to Space Needle toward the end of the day. From there, you can see where other attractions are and other potential places to visit. So we went on the Giant Wheel (this is the Ferris Wheel that you sometimes see in color shots of SEA before games). It costs $17, not on Citipass, but again offers great views of what else to see.
Having gotten bearings, the next day we went to Seattle Aquarium where I finger wagged this seal that came right up. No fish here seal. Then went on the Argosy harbor cruise that again pointed out additional attractions among them C-link. Saw the Pop Music Museum everyone raves about. IME it was the least impressive unless you are a die-hard Jimi Hendrix or Pearl Jam fan or into Marvel (I didn't pay extra for the Marvel). Ended up at the Glass Museum next to Space Needle.
We also went to the public market, which along with fish also has a lot of individual craftsmen selling stuff. I bought an individual glass piece (OK, it was a pot pipe) that was not only beautiful but optimized for functionality. And as Washington\ is recreational, there's also a dispensary in DT SEA that just requires ID to buy, and they take out-of-state IDs. Across this market a couple of blocks are stores that sell Hawks gear. Got Hawks tennis shoes for $15 at one. There are also a number of comfortable seafood restaurants, but they are not only more expensive than the fish market but also autoadd a 20 percent tip.
There are also lots of casinos in the SeaTac area. The one in Snoqualmie is the closest; it's about 30 min from DT SEA. They have a really good gift shop with lots of Hawks gear that's not ridiculously overpriced. The only complaint I would have about them vs. Reno is that I couldn't find the sportsbook.
Yeah it rains but not all the time. It is definitely more walkable and generally easier to get around than places like SF Bay Area, and unlike DT SF, there are minimal concerns about stepping in or around human waste.
