I think something being missed here, and a major contributing factor to the mkiv Supra's popularity, is that it wasn't superseded with a mkv and is still the best available Supra you can buy.
I have been thinking about this for a while, trying to decide what to replace the Supra with.
I think alot of other cars popular with petrol-heads will struggle to reach the same legendary status as there is often a better, more modern version available or in the pipeline.
I like R34's but would always really want an R35,
I like the 350z but in a couple of years when the 370z has been on the road for a while it will probably look dated and I would want a 370. And so on.......
The mkiv Supra was and is the pinnacle. Nothing else replaced it therefore there is no natural progression onto something similar but better.