I stayed at the SEA airport Marriott about a year ago on a $59 rate. I the price was fair.
If you plan on staying there, avoid any room facing the indoor pool. It is located in a large multi-floor atrium and the noise can be horrendous.
On weekends, the lounge is closed. The breakfasts coupons given to Gold/Platinum entitle you to the Healthy Start buffet which was quite nice.