Thank you for the suggestions. I've already added a few more circling Mini-Puffers in the desired locations, but I'm pretty sure I've already made a significant enough difference between the darker palettes in the underwater segment and the brighter palettes in the beach segment.
Honestly, I think I've made my level about as great as it can be. I don't think I can make any more changes without going against one or more people's feelings about the level. In other words, I'm pretty sure any additional changes will make some people happy, but they'll make others frustrated. Plus, I need to admit, I really don't feel like posting a new IPS every time I make a few small changes to the level, as the free space in My Files is rapidly running out.
In short, I'm at the point where I really want to call my level complete (and I want it to be finished before my free time is entirely consumed by college). I've already posted the hopefully final IPS in the testing thread, but I'll put it here as well.
I don't have any major complaints. It feels more difficult now, it plays nice, and it looks/feels nice overall. If nobody else has anything to say about it in regards to improvements, then you can go ahead and PM me the necessary stuff for the level.