Quoted from Frax:Yes, KISS uses songs as "modes" but the goals are not really to FINISH those modes and start the next one (like AC/DC) in order to get to the wizard mode. You can pick a mode in KISS and not worry that you're totally effing up your point values, unlike ACDC.
Just for clarification on the KISS songs/modes...it is important to your score to finish songs because that's what advances playfield scoring to 2x, 3x, 5x, and 10x (Colossal). Even just getting 2x makes a HUGE difference in your score.