I think that people like the SS because it feels like a “real” Weber. It is built and looks a lot like the first Genesis gas grills with a strong steel frame. The stainless top is a timeless touch that further gives these grills the feel of a classic car. I have one waiting on a restoration and I also have one second generation Performer with the thermoset table which I have restored and modified after 13 years of use. (Even after 13 years my table is still in great shape.)
Comparing these two, I would say the newer one doesn’t feel strongly built, but it is fine if cared for and a lot easier to maneuver around. One of my casters rusted off, so I switched it to having regular wheels and axles on both sides. The grill is so light that casters don’t do anything for you, anyway. Now I can roll it down the street with ease in our campground community when we have events. So I like them both, just in different ways.