Don't really track it myself, either; I just try every tax season to stock up on tires and replace what needs replacing. Sometimes I don't succeed....
All I have to do to put a smile on my 'wallet' is to factor in what I DON'T spend on a car -- registration, insurance, tune-ups/oil changes, brake jobs, flush-n-fills, stops at the gas station. Heck, just gas & insurance have paid for the bike as of about 8-9 months ago!
The other, obvious-to-us benefits are priceless, so there you go.