I think it all comes down to the trade-off between more power, a shorter life span. Strongly correlated with that is the $ investment as well as the quality of the work & maintenance performed.
At the end of the day - assuming a realistic tune (on a limited budget) - the trade-off will always be greater wear and tear as 99% of us are on a limited budget.
So, really, you probably need to work this one backwards:
1) How long do you want the car to last?
2) How much power do you want?
Out of those two variables results the required budget. So:
3) What's the required investment?
Out of these three variables you could create a pretty solid (and simple Excel) function (using either a sample via questionnaire or good experience figures from Z experts like Sam) - but it would still not necessarily account for the quality of the work and maintenance done on the car.
Sorry, the post is a bit theoretical in nature.
