In my opinion - which usually tends to tick people off:
Yes, I say turn most of the parks into wilderness. Yosemite is no longer a "timeless area of beauty" and I do not need to escape from my world into a wilderness or national park. I like the world I live in, and my forays into the wilderness enhance my life.
I have been to Yosemite two times in my life. The first was in 1971, when I hiked from the southern most part of the Sierras to Yosemite. I did not go all the way into the valley, when I saw the smog and crowds. I turned around and went back home the way I came. That was also my last trip on the JMT and hike up Mt Whitney, because there are to many people on the trail. It is my choice not to return.
The 2nd trip was in 2004, when I took my son who was 18 at the time. He wanted to go, because it was a trip we had never done together. I did not see timeless beauty, but then I was probably wearing blinders. I saw pollution of all kinds; smoke, car fumes, noise, trash, etc. The animals are not wild, they are humanized and that is often their death. Too many people there do not respect the national park, because of the easy access. If they had to hike in, they would not go.
I saw defaced trees and rocks. I saw overused trails, cement trails, meadows mushed and compacted by boots, and trails sprinkled with litter. Is this how we preserve our national treasures for future generations?
I could go on, but I think my point is made.
As for access to all, at what point do we draw the line? Should we build a tram to the top of Mt Whitney and Mc Kinnley, because too many people cannot hike to the top? I live at the base of Mt San Jacinto, and rarely go there, because the Palm Springs Tram deposits thousands of people into the "wilderness" each year. This wilderness does not feel like wilderness. Trails are lined with wooden curbs made of dead trees, to keep morons off the sensitive land. Areas are roped off, because people have damaged them. Metal interpretive signs dot the landscape. The worse is "Meet Jeff" that is placed in front of a Jeffery Pine. Let the people buy a book if they want to figure out what they are looking at.
And yes, I can/do most of my hiking in the wilderness areas. That is what I have been doing for 40 years, mostly because of the points made above. If I venture into a non-wilderness area, I do it during the off season, when there are not crowds. But I am always sickened when I see the damage done by others. There are so many pristine places I can and do hike, I do not need to go into the heavily populated areas of our National Parks. I am fine with that. But our national treasures are becoming filthy Wal Mart parking lots with crime, filth, and a city-like experience.
With the population explosion, our national parks can no longer absorb all this abuse.