Glad to read this thread.
I remember the Hawthorne Muchachos (although they were disqualified in 75, I think), the Bayonne Bridgemen, and certainly the California Blue Devils (and many more, particularly for the DCIs). I played drums in high school (first bass, then snare). My buds and I went to these in the late 70s, when the popular theme seemed to center around anything Maynard Ferguson (La Fiesta, already mentioned).
A friend of mine tried to get the Bridgemen moving back into the groove for a while (after being a Muchachos alumni), he had a musical director role of some sort in the trumpet section at the time. The Bridgemen had attitude. Contagious.
Like it or don't like it, drum and bugle corps was (and still is) an exciting discipline for young folks with musical talent to get involved in. I've never seen such spirited people at that age working so hard to achieve. And watching them perform while knowing (or even just learning) the rules makes it a spectacular event and very credible competition. Those days I'll never forget, lots of fun.