In my opinion, and personal experience, there are diminished returns above a certain level of computer specs regarding PS/Lightroom. Games, top games, are designed to utilize a powerful system. So with games, especially the latest-greatest, you can actually see nice improvements when played on a higher-end system (faster fps, capable of higher resolution, better details, etc.). DISCLAIMER: I don't ever do games But I know that games can utilize a powerful system.
Photoshop/Lightroom/ACR however, not so much. There are some improvements in editing/processing speed on a higher end system but the difference is not night and day. The newest version of ACR actually lets you use the GPU to help out but it's not a huge deal, especially if you have a fairly good processor.
I just posted in another thread that after upgrading my decent system (i7-4771, 16gb RAM, GTX 750 Ti, HDD) to a better one (i7-6700K, 32gb DDR4 RAM, GTX 1060 6GB, Samsung SSD) I just didn't see a big jump in performance in Photoshop and ACR. I didn't expect one either though since I had researched and found that PS/Lightroom/ACR is not very good at utilizing higher end powerful systems. For example it's almost a waste of money to buy an expensive 6 or 8 core processor for Photoshop/Lightroom since most processes only utilize up to 4 cores. So generally a 4-core but high clock-speed processor may be better for PS/Lightroom than a 6 or 8-core processor but at a lower clock speed.
Video editing and encoding/rendering is different though, more cores are better there.