Well, at least JJ1's enemy toughness increase is noticable at any point in-game as it doesn't have weapon PU's, unless you count the RF missiles up-close as a 2x damage. And I'm glad to hear that the turbo mode stands open for new ideas! First things that come to my mind regarding 'behavior modifications' are an increased amount of projectiles for enemies such as the Hatter, and wider jumping patterns for the Fencer and Helmut.