The ethical thing to do is to point out the error. But, I think there should be a way to do it so that the good Samaritan is not put through hoops of bureaucracy. After all, you are not the person who made the error. So, I would write a letter, send it to the hotel manager (or corporte office), and be very clear about what the error is. Email is probably sufficient, but the best CYA is to send it with a return receipt. After this proper notification, the responsibility lays at the hotel management to make the correction. In the letter, I might even add a stipulation that if they do not make the correction in 6 months, then these extra points belong to your account.

It's easy to be ethical; what's hard to do is to get the right thing done.

If an extra $200 is credited to my checking account, I would notify the bank in the same way, by writing, but I would not stipulate that the money would belong to me after a certain period of time. The reason is simple--banks can go after you in nasty ways and they will get their money back, especially when they made the error. And don't expect a heartfelt thank-you either.