Many people think that a car is done at or around 100 K Miles, I think that's because many companies guarantee them for that many miles when they are brand new, but I don't think that applies to the 1968 BMW Z3 warranty.
At any rate, I should hope that a car as fine and upscale as a Z3 and /or other BMW's would last a long time based on the original sales price and the fact that many other foreign cars last much, much longer. I would also say, don't race the car continuously as well.
My wife's 2003 Honda CRV is at almost 200K and it doesn't burn any significant oil between service, both cars in my garage are using synthetic oil. My Z3 is at about 120k miles and I have no plans as of yet to replace it, I hope to have it a good long time, maybe 200k miles.