I have always maintained all signal chains as pristine as possible by NOT inserting or using any form of video processing to the native 1080P24 signal. I rely on the player to provide the original source material as it was transferred to the media and an accurately calibrated projector to display it with the correct color temperature, SMPTE color coordinates and gamma; no adjustments are made to it for preference.
However, I broke this lifetime rule after I saw the technical performance of the Darbee Darblet video presence processor. This small box provides outstanding improvements in detail and edge sharpness with negligible negative measurable or observable impacts to any test signals. Yes, it can be misused just like any other enhancement device and it will clearly show its negative presence, but with just a small amount of enhancement, I feel the positive effects to the perceived image more than outweigh any negative side effects.
There is currently no 4K version of this device and it is yet to be seen that when such a device is released just what kind of improvements it will provide.
The DVDO iScan VP50pro is now only used to provide technically accurate test and alignment signals over HDMI.