If you visit the MVCI web site and look at the resort calendar for Marbella, note that 16 August to 8 October falls in Gold season and the weeks thereafter to the Gold Holiday season. This basically coincides with when the hotter weather ( 80s ) finally abates and the daytime temperatures drop a bit (to the 70s ). This can also serve as a relative way to gauge when demand for weeks will be higher.
If you were trading a Marriott week for Marbella, I'd expect that you could get what you want (2BR) anywhere in the time frame (providing you have a comparable week to trade). I would expect some Gold inventory to trickle down from the II Marriott pool, but I don't know how your Sunterra points would stack up in those queues for those September weeks which might be in higher demand.
I concur with JohnP. If you have specific weeks or villa sizes that you must have, you might want expand your request to include at least Marriott's Playa Andaluza ( if the Marriott type of experience is mission critical ) or to other quality regional resorts to secure what you want.
I can understand Playa looking a bit messy, construction will indeed be on-going, but now towards one side of the resort. An on-site restaurtant will open around June. Just like Marbella, there are no restaurants within easy walking distance of the resort. But there are indeed places nearby that the concierge can direct you to -- check threads here or in the Marriott section. I would not summarily dismiss Playa if your villa needs are mission critical. It might be wiser to keep Playa on the table while you wait it out and try to snag your first choice at Marbella.
Happy travels,
Barry
