In general you can’t expect any such motor to idle for long periods of time without acting up. Plug fouling and loading up of mixture in the crankcase is more or less the nature of the beast. Use a trolling motor for trolling.

If compression is good, as it seems to be, and there are no bad noises, I would incline to put some effort into it. Cleaning up and replacing wiring is tedious but can be done bit by bit. It just takes the right materials and workmanship.
Carbs? One cylinder running lean can be fatal. Are the plugs all the same appearance? Fuel filter(s) clean?
Fuel? I don’t think E10 gas causes as many problems as get blamed on it, but it’s wise to check fuel lines for internal deterioration that could shed bits.
Just some idle thoughts……