Since you are only staying for two days and are only around the downtown area, I don't think you will need a car. Bus #194 connects you between SEA and downtown, and several buses (#3, 4, and 16) run between downtown and the Hampton Inn. You can also do a 10-15 minutes walk to Seattle Center and hop onto the monorail to downtown. It is fairly convenient.

My office is 3 minutes walk off that Hampton Inn (I drive by it everyday.) You come at the right time as the weather is pretty nice these few days!