All depends about the spare time..
But i think maybe can be a minimum of three hours a week (my Classic Amiga its not my main Machine anymore two years ago). Thats, maybe playing any game, browsing the Web, or doing different things.
Somebody talk about Commodore 8bit stuff. In my experience both machines work fine, i have several C=Commodore and C=Amiga Stuff and all work fine.. Maybe you not had the correct procedure to preserve the Amiga hardware.
Anyway, i could beleve the C=64 can survive any nuclear war becouse the Commodore 64 comunity its very active.