That's an interesting analysis and probably deeper than I could have gone. If I were going to pinpoint a year of change, though, it probably would have been the introduction of amps (and then later electronic instruments) rather than 2008. With that introduction, the potential for communicating a storyline increased dramatically, at the expense of the old "show, don't tell" mantra. Consider the Cadet's two-year Alice in Wonderland concept or their talk-show show.
An interesting result of this is that show designers now have a chance to make political and social statements that they couldn't make before - such as in Pacific Crest's show a few years ago which depicted the development of flight and then made (in narration) several social comments about war, etc. Carolina Crown's Bohemia show in 2004 ended up with completely meaningless beat poetry in it, but at the beginning of the year the poetry was much different, full of social commentary (which I imagine drew enough negative feedback that they changed it).
To me, these are not improvements. Shows are becoming more about the show designers and less about the performers. Play great music. March readable formations. Give me a guard show that looks like it's part of the whole corps show rather than a completely different production.
I find storylines distracting, especially when they feature guard soloists cavorting around the field for the entire show. When the story is presented more as an abstract theme (a la Phantom this year), that's less distracting to me. I can't follow a guard soloist trying to communicate a story and still watch the show as a whole, so I tend to ignore the guard in those storyline shows. An exception this year is Glassmen, whose show I really like - but the guard soloists in that show actually function as part of the guard for much of the show, making the story easier to follow.
The best example I can give of how shows are becoming more about the designers and less about the peformers is pre-recorded voice and other sounds. Seriously? Amplifying the performers is one thing (which I've learned to live with); giving them electronic instruments is another (which I'm still trying to learn to live with). But bringing in audio elements that have nothing to do with the performers? I'm astonished that ever got passed - major step in the wrong direction, IMO.
So I agree that it's probably pressure to be more competitive. It's also show designers wanting more freedom to do "whatever". (Did you ever read Hoppy's justification for the introduction of amps? No attempt was ever made to explain how it would improve the activity - it was all about the effects he wanted to create. The number of times the word "I" occurred in that proposal was astounding.) I get it, but I don't have to like it.
That said, I also agree that this year's shows are generally more entertaining than the last couple of years. In the early days of "wild west" (electronics), there was a sharp dividing line between corps that used it and corps that didn't - and those that used it invariably overused it. Now, I think corps are beginning to find a balance - a way to get electronics to complement the show rather than dominate it. Same with FOF (Furniture on the Field). With the exception of the Blue Devils and a couple of others, the FOF this year generally is not that distracting. I'd rather be without any of it - but I appreciate the balance that seems to be evolving.
I'm also interested to see how this all evolves. Ultimately, the financial pressure to place in the Top 8 will make scores incredibly important, so the only way things will change significantly is if the sheets change.