In Evo 500s, the Maicos are widely considered The Bike, and command a premium.
The YZ465s are the next best, and are definitely the best of the jap bike of the category.
They both go for good money because they're good race bikes.
RM500s are an oddity. They are super desirable now, even though they weren't considered that great in the day.
In contrast, the YZ490s were more popular when new, but are treated like lepers now...
Big bores are always sought after, esp those with disc fronts.
The last of the Evo Kawasakis seem to be very popular and consequently expensive, but it seems to be 50% race performance, 50% looks...
The 84 KX was a very clean, original bike. I think that lots of people would have bought them new but steered away because of the earlier frame breakages and parts supply. History has shown that the 84s were actually quite good, so the pool of potential buyers in 2011 is large relative to the number they sold.