0.5c/$ would assume 1 point per qualifying dollar of spend, if you value points at 0.5c each.

As a blue member, you get at least 10 points per dollar - so 5c/$ spent, plus you'd probably want to be on points+points rather than points+miles, taking it to 7.5c before any promotion.

If you then assume that you can get an average of 15 points/dollar of promotional value on top of that, you're getting into the 15c range, before you add any status bonuses.

So even as a diamond, valuing points at 0.5c each, your minimum return (before you add in the value of bonus points, breakfast, exec lounge access, wifi, and theoretical upgrades) is 17.5c per dollar on average (some promotions are more valuable than others).

While that might not be enough to sway you away from the best deal on hotels.com (if I'm paying Hilton $150 when an equivalent Novotel is $100, the loyalty scheme won't bridge the gap) it should match it if the Hilton is a viable choice.