There is a Marriott across the street from the Doubletree and actually connected to the Conference center by a walkway. It might be easier for you to get certificates from a Flyertalker for a Marriott. Any reason why you want the Doubletree?

I personally put my friends up at the Hilton so I can get the points. And when I have used Priceline I typically got the Hilton at a much lower rate than published rates (but no points).

For convenience of walking around Monterey, the Doubletree or Marriott are much better.

Also, parking is not free at the Hilton. There is an $8/night charge, but it is not gated so some people just park, don't tell the hotel they have a car, and don't pay.