Actually, I think they've gone downhill, but not quite for this reason. I'd be quite happy to see them act daring. But it seems to me that at the same time they've done this, they've tried to keep the viewers out of trouble by refusing to disclose the details of the experiment. One example is when they were doing "exploding pants", they wouldn't reveal the proportions of the various chemicals that they used.
I understand why they do this. However, for a show whose theme is supposed to be discovering truth by questioning, this attitude of "we know best, and you can trust us to do it right" seems wrong. And for me, it spoils the whole show.
I think you can thanks America's post 9/11 paranoia for a TV show not being comfortable with (or perhaps legally allowed) telling people how to make explosives.
So, the myth is "not discussing explosives recipes on TV reduces bad uses of explosives". Debunking that one in a safe & legal manner would be some Mythbusters I'd enjoy watching more than "exploding pants".
I think it's gone downhill because of a declining pool of good myths left to test (how many are basically just "someone on out forums dared us to do this" with a thin veneer of "myth").
I understand why they do this. However, for a show whose theme is supposed to be discovering truth by questioning, this attitude of "we know best, and you can trust us to do it right" seems wrong. And for me, it spoils the whole show.