Same problem. I think the real key is figuring 1) how you might use them, and 2) what you would spend if you didn't use them.

For example: Using 4000 Starwood points for a hotel room that costs $120 per night - they could be said to be worth 3 cents each. But if you could (or would) have used Priceline to book the same (or comparable) hotel for $40, they really are only worth 1 cent each. Some people don't figure that in, since they would never use Priceline - others do.

Generally speaking, Starwood points are worth considerably more each than Hhonors or Marriott points, I don't know about other programs.