Would it make sense to put 2 pinch clamps on every PEX fitting as an insurance against leaks?
I assume you mean two crimp clamp rings one after the other (i.e., side by side) and not one on top of the other. Putting on two clamps might trap water between the two clamps. Mold and bacteria could grow in this space. This volume would not be swept by flow and would probably be anaerobic.

Unless doubling up on the clamps is a described optional 'heavy duty' installation method, this kind of installation would be contrary to the instructions/specifications for the system. It could fail inspection.

If you wanted to do something which would improve the quality of the system, I think a much better approach would be to implement a system where each clamp connection could be inspected with the house finished walls in place. This might be small ports with inconspicuous covers. They could be so small that a borescope might be required.