I regret not starting earlier too. If I had, I would likely have gotten the Subatomic Supercollider and the Mapple Store (buildings I still don't have today) and other Halloween/Christmas items that I do have but had to spend donuts to obtain. The Mapple Store hurts a bit because I could have gotten it back when I started playing as it was still available then. I even had enough donuts to do so, but I had no idea it was going to be removed and thought I would have the opportunity later.
I have a bit of regret too about not getting the Fruit Bat-Man skin for Mr. Burns, considering it was from a fun episode, it is the only skin he has that is premium, and it is the only skin that actually has tasks at the Burns Manor (imagine that!!).
However, overall, I have so many characters and buildings now that it's difficult to feel like I really miss any of those.
