Amazingly what you are talking about is kind of the way the U.S. government works. The government was built in such a way that it would be extremely hard to ever change anything, and its made itself more that way as its gone along.
However, beneath the system, which I agree should be slow to change except in the most dire of circumstances, there needs to be freedom for the people themselves to move and try new things. Even if they are wrong or horrible, you need that movement or you stagnate. If the people themselves become part of the "slow changing" system, then what happens is you stop changing and you can't meet new opportunities or change when you should, so there is no "best" political party to be in, excepting the one that's right for you and your beliefs. Then, hopefully society can continue to be stable and move forward and the better ideas are accepted, not by individuals, but by the majority and the system over time.
The problem with this and you idea is whether inherently, the majority of people can be correct always. I think you'll find several examples through out history where the majority have simply been wrong. And for this reason, I don't buy into what you are saying completely, though I do agree that for a mode of government its better than some instable flip floppy machine that goes haywire when it sees a pebble on the side of a mountain.