This thread really intrigues me because I have been researching Marriott Grande Vista vs. DVC (both resale). I have seen advice all over the place regarding the saturation of non Disney Orlando based timeshares and their ability to trade. That being said everyone says not to buy DVC if you plan to trade and that trading into DVC can be impossible unless it is off season. This would leave me to believe that a quality timeshare like the Marriott resorts in Orlando would be in reasonably high demand if low numbers of DVC units are available. Am I wrong? Also, I would love feedback from people who own/use both the DVC system and Orlando based Marriott resorts.
I wouldn't buy a Marriott in Orlando, but I would buy DVC. I love Marriott's Cypress Harbour and agree with the OP that CH is superior to any other resort nearby, but it is also an easy exchange with a decent trading week. I save a lot of money by trading into the Marriotts and the DVC resorts with my quality exchange weeks, and I saved a lot on the purchase, plus my maintenance fees are lower than the fees at the Marriotts (or DVC).
I would buy DVC, and plan to sometime, just for the AP discounts. $100 off per annual pass is worthy of a purchase. If I buy just 50 resale points, I can get us all annual passes for that discount, and we can stay in a one bedroom for 5 weeknights every-other-year. I know Rick will eventually let me buy those points.
I get DVC. I love the theming, the locations (Rick's favorite is Wilderness Lodge Villas, where we stayed last year for two consecutive weeks through exchanges and bonus weeks with II), and the transportation into the parks. I love it, but our daughter and her family just spent a week in a two-bedroom (we had a one bedroom for two weeks) at Boardwalk Villas last month, and she thought it was just okay, only slightly better than a hotel room.

I loved our unit, which was two floors above hers. I appreciate all the perks and love the decor.
While we were in Orlando, we visited all the Wyndhams: Cypress Palms, Star Island, and Bonnet Creek (we actually stayed in a 3 bedroom at BC and LOVED it). Our daughter thought all of those were better than DVC. Star Island is really nice, I admit, and Bonnet Creek has very luxurious units, even the regular 3 bedroom was very nice. I understand why she liked them more, but I disagree. I would take a Disney over any of those, but I am equally happy at Cypress Harbour, I admit.
I love Cypress Harbour. Too bad I couldn't get a week there for December 4th. I took an MGV two-bedroom for that trip, and now I regret that decision because I could have had Cypress Harbour, if I would have been more patient.

I suppose II won't switch me without another $139 fee).