The box our 24" iMac came it is like a fortress. Very good and protective packaging, lots of well packed cushioning.
That said, I'd wonder if the shipping charges you are talking about might be a good fraction of the cost of the iMac? And yes, I would absolutely insure it for its full value.
We have a couple of older MacBook Airs and that's what I take on trips. Very portable, can easily carry on airplanes and use to do work or watch movies, etc.
A new M1 MacBook Air starts at $999 and a new M2 MacBook Air starts at $1199. I am guessing that shipping of a huge iMac box (round trip) plus insurance will amount to a significant fraction of a new MacBook Air.