I have finished all of the events (chemical spill, dive trip, etc.) that are worth 15 bux each on Pocket Planes. I'm wondering if it's possible to reset all of it to 0 again so that I may start over from scratch.
No you may not, without resetting the entirety of your data and starting over.
Wow, well done, that takes quite a while!
I think that if you change GameCenter accounts you can reset your accomplishments, which will reset the counters for each of the 12-hour special events to zero. That is, create a new GameCenter account for example and then it gives a message about reseting achievements and also I believe the event scores. I did something like this inadvertently a while ago (it reset the event counters but I still had my full fleet of planes, parts, and cities) but it sounds like it may help you achieve what you want.
Note that you need not have the same iCloud account (where you purchased the games and so on) as active GameCenter account, though those both use AppleID. It could be a pain to change back and forth regularly if your GameCenter account is useful for other games.