Is the seat pan substantial enough that the seat could be rebuilt with more foam and a new cover?
I'd say you could. It doesn't have a massive amount of flex to it so I'd assume you'd be perfectly fine redoing the foam and cover. The current staples holding the cover on are spaced about an inch apart so you'd have quite a bit of space for new staples in non-holey areas.
The seat's only about 2.5 lbs which seems too light to me. The plastic almost feels like a hardened injection foam. There's almost a velvety texture to it, and not a hard plastic texture. It's also matte in color and not shiny which is odd for black plastic. The OEM seat is definitely a harder plastic, and I just weighed that seat and it's only about a half pound lighter than this zeed one, lol.
Although in saying this, I took off the seat just now to see if there was a drain hole or something I could use my micrometer on to give you a thickness of the plastic (there wasn't so I can't help you there), and saw that there's already breakdown of the plastic from where the edge of the gas tank lip hits and appears to be rubbing. The issue with this seat is the tiny bracket that slips under the gas tank, as it's only 7/8", which I why I had to add the rubber shims, and there's no way to bolt it down in the front. But now it looks like I may have to add some other buffer as the metal of the tank bracket will just continue to rub due to vibration and movement of the seat, which will at some point make a hole in the plastic. I've only had the bike out maybe 8 times, for about 30 minutes each, since putting the seat on so this doesn't bode well.
EDIT: Added a side by side of OEM (left) and Zeed (right) seat so you can see the plastic difference.