It depends a lot on how you use them. There is no set value. If you use them for a hotel which doesn't need many points but is expensive on cash, then you get much more value than if you use them for a hotel which wants lots of points even when it's relatively inexpensive on cash. That doesn't mean you'll find both extremes in the same search, just that in some situations (perhaps places most people don't redeem points?) you might very different value than in other situations (perhaps places where "everyone" seems to want to redeem points).

And it's constantly changing, especially now that IHG has started introducing Dynamic Point Pricing. Which means that values determined last year may not work for the future.