Interesting thread, but too long to read at work so forgive me if my comments are redundant. My buds and I (all old turds from the turn of the 80s) have been having similar discussions. I didn't see any drum corps from about the mid 80s to the early 00s so I was in for quite a shock when I came back.
IMO, the only difference between drum corps and marching band has always been powerful brass. That's what got me involved in 79 after hearing Spirit and Madison live in 77. Could be my hearing going but that aspect of DC is just not there any more. Maybe it's the move away from G bugles, maybe it's the super demanding drill, maybe it's due to a deliberate move away from being loud because we can. I don't know, but I do know that for me, shows today aren't as musically entertaining as they were when we dinosaurs roamed the earth. Definitely more technically demanding, the kids today could play circles around us 2 valve hacks. But nowhere near as goose-bump-raising, hair-on-the-neck-bristling entertaining.
I always liked watching precision rifle work and for the most part, that's gone as well. I don't like ballet and to me that's a lot of what todays guard has become. I can appreciate the athletic ability required but it just doesn't interest me.
Most of today's shows bore me to tears. Granted, there are some moments in some shows that are neater than grits, but nobody recently has had a show that kept me on the edge of my seat the entire time like they used to. And I saw most of the top 12 at some point this year so it's not an isolated sample.
I too am thinking of passing on DC in the future. I'll just go watch my son's HS band contests (mandatory as a parent) and be bored there.
That said, I LOVED the Cavies in 2006. Go figure. Maybe I'm just full of bull butter.