[Perfectlap]

funny I never do the the rear window chop and I have no crease at all.

Let it do it by itself correctly, leave it down for a long while if you can. I think after time it just remembers where to fold on its own.

As for replacing the top, you never need to replace the top with some care.
Raggtopp on the canvas. rinse it weekly with a stiff stream of water and blot it dry, that'll keep the spray on protectant from coming off.

For the window use Plexus regularly (spray onto the towel not the window to keep the Plexus off of the canvas). I also use Plexus on the windscreen and headlights and tails.
Every few weeks (if driven daily) use Renovo polish to remove hairline scratches and bring back clarity.

and of course the softop cover from Ebay when you are parked outdoors can make your top last well you may never need to replace it.

As far as plastic window in general I've seen them on Ferraris.
So don't feel bad. The Miata design guys are just really smart.