I also had the 3 tube horizontal model with a 7' screen. I think I paid just under $3k for it back in 1977. Paid $750 for that Magnavox laserdisc player as well. It wasn't very bright and demanded full darkness in the room. The curved screen gave a very small sweet viewing spot. That was good for a single engineer. I used to run tech for the local community theater, so we had a few cast parties at my house centered around the projector. Kinda nice to be bunched up around all the young wannabee actresses
As I said, I got transferred to California in 1981. By then I was married and expecting our first child, so I sold it to a friend. It was working perfectly. He continued to use it for another 5 years. I didn't put together another front projector system until the current one, although I did have several rear projectors.
I bought the current setup at a time I felt the industry had stabilized on 1080p and the new audio codecs became available. I knew 3d was on the horizon, but decided I could live without it. I've lived through several previous pushes into theatrical 3d and generally find it wasn't worth it. We have been satisfied with 2d versions of most of the 3d titles.
The way I figure it, my next upgrade will be to 4k. I will consider 3d at that time, but it would be a want, not a must. Kind of the same for ATMOS. I see it as evolutionary, but not revolutionary. I can definitely see the advantage of 4k on the big screen though and will look then. But that won't be until HDMI/HDCP stabilizes and the next generation of projector tech is proven. Oh yeah, and the early adopter price premium goes away. Probably 3-4 years.