I calculate nothing. I spend what it costs to buy a game and that money is spent/burnt/gone.
When I need to repair, I spend what it takes to keep my games functioning - this is very important to me.
To answer your initial question about philosophy - I buy my games to keep and they are not going anywhere - hence any tracking of costs is irrelevant.
I'm in this for the amusement and enjoyment - and the money doesn't figure into it.