Marriott Rewards redemptions for me have been consistently valued between 1 and 1.5 cents per point. I redeem mostly lower to midrange awards, and I've never squeezed much more than 1.5 or 1.7 cents out of a Marriott point (based on the best rate I could get paying for a room). However, considering the fact that Marriott gives me 12 (I'm Silver) per dollar spent, that is a pretty good reward.

As for the Marriott for $50 a night: What property and what nights? Did Priceline make you jump through any other hoops to get the rate? (apply for a credit card, etc.) Obviously, incredible deals show up once in a while, just take 'em and smile. Of course, Priceline stays probably don't earn points or count toward status.

You'd never value your airline miles based on a $100 cheapie ticket you got on the Internet, so you shouldn't do the same with hotel points either.