Upgrade the projector or projector screen?

I actually have the Stewart Filmscreen StudioTek 130. It has a very very slight texture to the surface of the material. If your Screen Innovations surface is perfectly smooth, I can sort of see how you would think the Stewart "looks" smoother on video. I think the texture on the surface acts to break-up the separation between pixels - as the LCD pixels do not have a great fill factor. If you look closer, you might get a "screen door" affect where you can see the pixel grid. If you wanted to smooth out the effect of your current Epson LCD, the Stewart -MIGHT- help fix some of that pixelization roughness. I don’t know for sure. You can also solve for this by very slightly de-focusing the image so that the pixels sort of flow into each other.

The JVC DLA and Sony LCOS panels have a much better fill factor - you will get less of the screen door effect. I have an older Sony VW95ES 1080p that I just love. To this day, I have not had any urge to replace that projector. Though, it does have a color calibration using Lumagen Radiance processor. If you’re not worried about 4K output, Curt Palme website is selling the Radiance 2020 for $1399.