If the numbers of people attempting highpoints decreases in the future, it will NOT be, IMHO, due to high fuel prices or higher CAFE standards. We just bought a new Prius that gets 43+ mpg, which means we can go a LOT longer on the same amount of fuel we got from our old car.
I think that if we do see a decrease in the future, it will be because at least part of the younger generation (can't believe I'm saying this) is far more inclined to experience the world vicariously through video games and such, rather than getting out there in real life, which I would consider being due primarily to the present generation not educating and exposing their children to that real world. However, my own experience with my own daughters and their friends is that they tend to be far more open to travel, outdoor adventures and such than I was ever able to do at their age. I didn't have the time, money, or, in a broader sociological sense, the permission to take the time to experience the world. I never traveled more than 200 miles from home all the time I was in college. My younger daughter has already been on four continents!
Yes. Virginia, there will always be highpointers! And with the advances in transportation, equipment and communications, plus the eternal desire of so many people to see "what's over (or on) the next hill", I feel sure the Highpointers Club will continue to recruit members for a VERY long time. Sure hope so, anyway!