IMHO, I don't think you should ask your friend for anything, and he should offer to treat you to a nice dinner or something like that.

Half of the $300/night is definitely not right, since the two of you would never spend that much oln your own.

I don't agree with half of the $150/night since that's not what it is actually costing you. Most of the points were free from other hotel stays and credit card spending. I'm guessing you didn't spend to much actual cash to accumulate those points (I know all about the argument that you may have stayed at a slighter more expensive hotel to get the points, etc. but I don't find that a compelling reason to charge someone money for something that is basically free).

I feel you shouldn't ask for anything from your friend for two reasons: (1) He's obviously a good friend if you go away every year, and (2) you offered to use your points.

Hope I didn't offend you but that is my opinion.