If I were doing it, I would just do it based off of what the best rate was for that hotel and what portion of it that person was responsible for. IF it were a great redemption value (ie... great return for your points... then it might not be fair to ask the other person to pay a normal share of the room rate because you obviously chose a currency - points - to pay for the room because you thought that was a better deal for yourself as well... there is no real reason to seek to profit from your friend and I don't think you were trying to... which is why you came here to ask about point value.)

Ignore the other people. Just like someone said life is too short to worry about every penny... life is too short for you to either care what these people are saying about this or for them to care how you use your points. They are your points, so it is your right to use them as you wish (subject to complying with the terms of the MR Program).