My/Wife's IS200 is now 8 years old and apart from a replacement shock absorber has been fault free. It is still a superb car to drive, doesn't squeek/rattle, no rust. It's negative points, MPG and wayward back end if pushed in wet or even driven on snow/ice need to be considered. The bad MPG is cancelled out by the mammoth cost of changing it and, of what I have read, I will change the back tyres to Rainsport 2's ASAP.
There is therefore no compelling reason to change it. I think that it will be many years before it becomes a classic. There are simply too many of them.