I don't know if I would say that Doyle is fascinated with the high end of the spectrum, just that he is more willing to go there (and occasionally stay there) than many other composers. He is also willing to go lower, as a listen to HENRY V, DEAD AGAIN or FRANKENSTEIN will bear out. And I would also add, he is willing to go faster; I'd be willing to bet that the average tempo of a Doyle score, of any genre, is slightly brisker than most other composers, although he has mellowed out a bit in that respect over the years.
In any case, thanks for the observations - it's interesting to me how everyone would agree that Doyle has a distinctive sound, but nobody ever attempts to deconstruct it. (In fact I'd like to read more such deconstructions of many different composers)