I've never had any difficulty using MR points for villa stays, but I tend to book fairly well in advance (at least 6 months or more). I've currently got a week at Shadow Ridge in Palm Springs booked for Easter week on points - I booked that one a month or so ago.
The one restriction is that if you roll your week(s) to points, you can't use those points to book a stay at a Marriott timeshare. They keep track of that information somehow, although whenever I look at my balance, it just gives the total number of points and doesn't distinguish the source of those points. Perhaps if you call them they can give you the breakdown.
Another thing to consider is to use the Marriott Owner's Discount code (MOD) and see what turns up. We use this all the time at the various Orlando timeshares. The rates we get with this code are so good that it's not worth it to us to burn our points - we'd rather pay cash.