You may not have a very accurate opinion of what it is like to be 80 years young! I went with my Dad to WDW for the first time in 2003, when he was 74, and took him on RnRC! He survived it better than I did! Though I like the music better!
That said, I don't worry too much about using my DVC in my 80's. I still think I will want to go to WDW, but I don't consider owning DVC to be a key component to my retirement plan. If I planned well, I will be able to replace it and if I didn't plan well, I probably won't be able to afford the plane fare and tickets that go with it!
-- Suzanne