SPOILERS (But seriously, the expiration date on this movie is long past, and it's worth watching even spoiled)
That is very interesting, and it makes sense, about as much sense as anything you can get out of the film. On the other hand, there are enough hints in the movie to lead me to speculate that the entire story was a psychotic delusion, but the question is, who's delusion was it? Can't be Donnie's because he winds up a corpse. Perhaps Frank's? Anyway, it's probably the wrong interpretation considering how the ending plays out, but on the other hand, the alternate universe explanation negates the psychosis aspect and also doesn't explain some of the movie's events, e.g. burning down the mansion. This seems more psychotic than anything; it doesn't seem to push toward collapsing the alternate universe. The only real consequence of the burning is that Donnie's mom goes to California for the competition . . . *epiphany* . . . and if she hadn't, then the party would not have happened and Gretchen would not have died and the universe would have ended. I had previously only considered the aspect that the plane would still have been flying over the city regardless of whether Donnie's mom was in California; I hadn't thought about the party. Still, I could see the events leading up to Gretchen's death happening even without the party, so it's not completely explained.
Flooding the school is much more easily attributed to saving the universe--without that happening, Donnie wouldn't have met Gretchen, and then the whole thing would have been thrown off. The idea that Gretchen was manipulating Donnie throughout the film the same way that Frank was is at the same time amazingly creepy and totally awesome.
That aside, I think the single aspect I most appreciated about the film was the craftsmanship. Every single scene and event in the film was carefully thought out and placed. There are set-ups and pay-offs galore, all of them well done and well executed, some even gut-wrenchingly so, e.g. Mrs. Death constantly wandering in the middle of the road being the first that comes to mind.
Of course, I'm not sure I appreciate some of the film's messages. There's a lot of Christianity bashing in the film, but the particular brand of Christianity the film takes on is laughably one-sided. It was a straw man argument, not something worthy of debate in the film. The only reason it was tolerable was Donnie's own internal debate on whether God exists. He is truly torn and for good reasons. Without his real questions and beliefs, I think I may not have liked the film so much.
In sum, as I stated earlier, the film got me thinking more than any movie has in a long, long time.