I have three points bookings out there in Cayman Islands and Dominican Republic. All have gone up slightly since I booked a couple months ago - none more than about 5%.

I am not a fan of dynamic pricing for obvious reasons, but one thing you can do is watch your bookings every month or so and often you can rebook for less. Have done that a few times in the past (with other reservations). I usually do this when I have enough points to make the new (lower points) booking before canceling the old.