I have amassed large collections of laserdiscs, DVDs, blu-rays and digital movies over the years. I still have 400 blu-rays and many still look and sound great. That said, I am REALLY enjoying the 4K disc experience. HDR, 4K resolution and Atmos make for a immersive experience coupled with my projection system.
As for buying habits, I am now disciplining myself to new films that are guaranteed multiple viewings (Star Wars, Marvel, Greatest Showman, etc). If it's a film I won't watch in the first week or two of purchasing, then I can wait. After being almost exclusively digital for a couple years and buying codes for $5 a pop, it's hard to justify paying over $20 per movie again unless it will be in heavy rotation. Somehow I have managed to avoid the steelbook craze which has probably saved me thousands.
I will definitely look to upgrade some catalog favorites around Black Friday when so many titles will be in the $10 range. Anything with solid PQ and an Atmos track is worth an upgrade for $10. I expect all the Mission Impossible series, the Jack Ryan movies, Braveheart, Gladiator, etc to fall in this category.