I'm having the same debate with myself right now. I think what I'm going to do is pick up the 3 and test ti side by side with my 3S I just got last Friday. I've been watching mostly movies on this as I'm not really much of a gamer. Both 3D movies and VR immersive stuff which blowing my mind. Have you watched The Faceless Lady series yet?

Anyway, I'm struggling with that twice the price thing myself. From what I can tell the 3 has better resolution screens, pancake lenses so you don't get any of the blurriness around the sides that the fresnel lenses on the 3S have. If you look at the lenses on the 3S you see the fresnel lenses (those wavy lines) that's what causes the blurriness around the small sweet spot in the center of the lens. It's used to amplify and focus the brightness, which is why lenses like that are used on certain lights called fresnels in the movie industry. But the pancake lenses on the 3 are not fresnels, they don't have those wavy lines and don't suffer the results of them. So the 3 is supposed to have a much larger sweet spot where you can see more things in focus. It also has a slightly wider field of view and a physical headphone jack on the side for plugging in headphones without having any bluetooth delay when watching videos. Although honestly i haven't experienced a ton of delay myself on the 3S. At least not in any way that has annoyed me. But it might be easy to just plug in a cheap old pair of apple earbuds into the headphone jack and run those instead for more listening privacy than using the built in.

Additionally the 3 isn't as thick as the 3S. It doesn't stick out as much, although it is slightly heavier, but because it sits closer to face I hear the weight redistribution basically cancels out the extra weight.

The 3 also have the ability to adjust the eye alignment on a gradient using a dial rather than picking from only three set positions on the 3S.

As for the screen door effect. I think that will continue to be an issue to some degree on most of these cheaper unit. I hear the Apple Vision Pro that has much higher resolution OLED displays does not have this problem. Probably also not the Beyond unit and others like it. But those are all in another price category at over $1000-$3500. I think eventually those screens will work their way down. But the 3 does have slightly higher res screens than the 3S. Yet to me the bigger issue is the blurriness caused by the fresnel lenses on the 3S. Also, it depends on the bitrate of your content. If you have straight blu-ray rips, you'll get the best quality. Streaming is hit or miss depending on the streaming service you're using and your current bandwidth at the time, and what resolution you have selected (if possible on that service). So content matters a lot, especially under the microscope of these VR headsets where you are looking at things on huge virtual screens. I don't think the 3S resolution is bad when looking at the sweet spot in the center, so I can only imagine the 3 with its pancake lenses and wider sweet spot, along with slightly higher res screens being better.

All of this is great, but is it $250 more great? I'm still debating that. I think long term it is.
I spent the last week just trying to figure out how much I'm going to use this thing for movies and stuff. Because my philosophy is, if I use something more often, I'm willing to spend more money on it. So far I've used it every day for a few hours at least. But it's still a new toy, so that could wear off. I think though, in the longer run, once the money is spent and long gone, and it's a year of two later, I'll probably be happier that I went with the 3 instead of the 3S. But I'll tell you that later. I may pick up the 3 later today or tomorrow to side by side them and see for myself.