Good point, cause you really do wanna keep all your powerups thru the levels...but that being said, i've still gotten decent progress even continuing on stages as far as 5 & 6! Red and blue can still be usable at lower power levels as long as you crank that turbo up to max!
Hidden 1-Up: right after u take off on stage 1, fly straight to the bottom left or right (sorry, haven't played in awhile) and drop a bomb. Voila, you'll hear the 1-up sound!