The biggest upgrade I ever made was going from an old Meade LXD75 8" inch Newtonian to a much more expensive SkyWatcher Esprit 120ED Triplet APO refractor. The differences were stunning. Finally I was getting round stars and I didn't need to worry about collimation anymore. I had the Meade 8" SN for 10 years, I don't think I've ever been able to properly collimate it. You see, with refractors, the optics are fixed and don't need to be adjusted at all. The Esprit 120ED comes with a triple set of lens, and focuses down all the visible light spectrum down to a focused point on the camera sensor. This means round stars and color accuracy, something I was never able to achieve with the Meade. Of course.. the price difference is spectacular as well.
But time had passed with the Esprit 120ED and while some images I was quite satisfied with, I was still getting some extremely noisy images, particular with this galaxy target: M101. I spent 3 hours on this target with the Canon 60D DLSR (astro-modded). I broke down and purchased a lightly used ASI1600mm mono astro camera. It was impossible to find this in stock thanks to being right in the middle of COVID-19.
The first night blew me away, with just one hour, I got way more light and less noise compared to the DLSR. The difference was staggering. It made me wonder why I stuck with DSLRs for so long. I understand many recommend it as it's easier on the budget, but these days you can purchase astro cameras for incredibly cheap. If you're a serious astro-photographer, why bother? I wish I knew about these differences before.
Comparison shot: Left is the ZWO with 2 hours of exposure, and right is Canon 60D modded with a little over 2 hours of exposure at ISO 800. No filters used for either of these sessions and sky conditions were identical. (Note: This ZWO camera is cooled, and was at -20C)