I use 1.5c/point - my baseline being the Grand Hyatt in Manhattan. I'd be willing to pay $225 including tax for a refundable weekend night there, although their AAA rate is usually a little higher than that.
(For comparison, I value SPG at 2.3c and Hilton at 0.6, which is close to the 3.9:1 ratio which AMEX Membership Rewards has for them.)