Personally, this would worry me. Since you checked, you are able to cancel your other reservation and keep this new one. But what if you never checked? The system would have automatically pulled the points from your account a week before the reservation and maybe you would have noticed that little action. If not, then you would have been deemed a no show and your CC would have been charged for one night's charge.

I have no problem with Marriott being proactive. It would be great if they saw that I tried to make a reservation, but couldn't and when availability opened up, they could contact me via phone or email to check and see if I still want that reservation. If so, then make it. If they can't contact me, then don't make the reservation as I may no longer need or want it.