Great questions!
I was hoping to compile a list of carts features by year and options / improvements for each so that I could better compare apples to apples and figure out what year would be best to meet my wants.
Newer is not always better....
I know (so far) that I am wanting:
Fuel Injected
Performance package (or equivalent) - this means it will go up to 20 MPH
LED lights (front / rear and side marker)
Retractable seat belts
10-inch wheels
seat upgrade
probably no more than 6 - 7 years old (but I am unsure here)
I am also still uncertain about the side curtains or hard sides (like the Curtis Cab)