I am 24 years old. I am glad that Disney constantly evolves so that it is always fresh. However, I think that part of what makes Disney World so wonderful is that it has so much more than thrill rides. Quite frankly, that is why I love it so much. I do not like thrill rides, and there is so much that I can still enjoy at WDW. Contrastingly, there is nothing at all for me to do at a regular amusement park like Six Flags.
I very much enjoyed some of the old attractions, but many of their replacements are even better, in my opinion. For instance, Mr. Toad's Wild Ride was a fine attraction, but I enjoy Winnie the Pooh much more. And judging by the long lines at that attraction on every trip I take, I'm not the only one, LOL! Of course, there are attractions that didn't necessarily change for the better. I think Disney realized that with the Journey Into Your Imagination, so they brought Figment back.
There is certainly value in keeping the classic attractions as well. For example, what would Disney World be without the Haunted Mansion? It's classic Disney at its best. The Carousel of Progress and Spaceship Earth are two other attractions that I hope Disney does not close.
I hope that Disney continues to have a nice mix of attraction types so that everyone can find something that appeals to them. There are some incredibly well themed thrill rides, interesting stage shows, classic attractions, slow moving attractions with unbelievable themes, etc. That variety is what makes WDW so wonderful.