The value of ECC memory has little to do with how long your computer runs or how frequently data is accessed. Restarting a computer won't prevent the problems that ECC corrects. ECC memory is designed to detect and repair memory corruption caused by electrical/magnetic interference or problems with the memory hardware.
ECC exists to prevent data corruption so that you don't have to restart your server.
Since I imagine you restart you iMac near daily, not having ECC isn't a problem.