I'm the guy driving
the red Italian
Join Date: Oct 2010
Location: United Kingdom
This question vexes a lot of people. The way I rationalise it is by using a fixed annual budget figure with which to own and run a car. I tend to buy older more interesting cars, even for commuting so I use £1000 a year as my budget. I don't include tax or insurance on the basis that I'd have to pay that anyway.
I bought my Spider just over a year ago and almost immediately changed the oil & filter and had the belts, tensioners and variator renewed. Then I replaced the radiator and thermostat. Luckily I'm able and equipped to do quite a range of work myself.
Dividing £1k per year into what I've spent in total tells me that on 14 Feb 2013 the car will "be worth £0 to me" so monetarily I could dispose of it without a second thought.
The nerdy spreadsheet I have with all the info tells me that the car is "worth" £1300 to me today so again, if someone offered me that for it, I wouldn't feel out of pocket.
A small patch of rust requires attention. Paying to have that fixed will merely extend the ownership period if choose to keep it or keep the price higher for longer if I'm thinking of selling it.
All this is purely a financial justification for owning a means of transport. It doesn't take into account the sheer joy of seeing it on the drive, let alone driving it.
Hope this helps.