In Singapore, it makes economical sense to drive your ride as much as you can and ditch it for a new one whenever your ride needs major change of parts.
An example of the S15, annual road tax is about 400pounds, insurance is about 1000pounds (full w/o no claim bonus) and the depreciation per year from new is about 3000pounds. So a full annual cost to keep an S15 is 4400pounds w/o any running cost tabulated yet.
I believe in conserviving milleage for a ride I wish to keep for a long period.
I also do think that spares can be a concern since the S15 isn't an officially imported Nissan from the agent. Parts can take a while to come by if required isn't common Nissan bin parts. OEM Nissan parts are cheap here.
For aftermarket parts...it is a different animal all together. For commonly worn and need replacement parts: The HKS Hipermax coilovers cost 600pounds and oem shocks would be 200pounds at most to replace. Pigid pads cost 300pounds and AP racing disc cost 300pounds per set while oem ones cost 30pounds and 100pounds respectively. A piece of Bridgestone S-03 255/35/18 tyre cost 140pounds while oem size of 205/55/16 of respective make cost 30 pounds each. So running cost can be considerable for a modified car in my country. And any aftermarket clutch disc will cost 2-3 times the price of the oem part. So if one puts 40k km a year, the replacement cost for the above would be say, 4000pounds in one year. Perhaps it is different for oem to aftermarket parts prices in the UK, but for me in where I am, aftermarket parts certainly cost lots more! That is why I did not wanted to alter my Murano since it is a daily driver and a family car...except for the 22" wheels. But the cost for a piece of conti 285/35/22 is 250pounds still hurts for running cost.
Besides cost matter, I cannot take the daily punishment from my S15 stuck in a traffic jam after a full day from the office. The fuel pump wines, the exhaust drones, the clutch is relatively heavy, the hard suspension so often causes my right foot to jerk the sensitive throttle in slow traffic....errrrrr. But on a bright and cheerful sunday morning, a spin in my S15 eases all the stress at work for a whole week....what a joy!