I've dug through a few prototypes and through the final game, and found some stuff. Stuff from the 510 prototype: Spoiler
Spoiler Stuff from the final game: v0.02 prototype palette for Palmtree Panic present Unseen prototype palette for Palmtree Panic past ...which fits better with the v0.02 background
Nicely done. I think the unused special stage layouts in the 510 have been found before, but the extent of the documentation was "hey there are unused layouts". Somebody wiki all this up.