I have. DH, DS4, DS2 and I are going on the 21th for 4 nights at Poly concierge. Based on my calculation, I think we are paying approximately $300 a night. We went the week before last Xmas and stayed at Sugar Loaf (Concierge Lite), GF for about $250 a night. We booked that trip through American Air. The difference in season--value vs. regular--probably explains the $50 difference.
My guess is had we booked through AA again, we would have paid about $300 as well. I don't think Dismey Visa offers the best bargain. I do believe, however, the discount offers come out for the cardholders before they get released for the general public. So if you are going to buy a package anyway, using disney card may get you wider choices in resort selection. Would I use Disney Visa again? I'm not sure.
We are talking about going again in November, so it might have been better to have gotten APs. Then, we hadn't planned on this trip at all. My DS2 asks his father one day in March if we can go to Disney World, and my DH says yes. DS2 then goes to his room, packs his toys in a shopping bag, puts his Mickey ear hat on, and waits by the door! DH got on the phone with Disney Travel that instant.