The use of four colors really makes the slipcases look terrific! I think you have the process perfected I hope you don't do like I oftentimes do and loose interest in craft projects once I've figured out how to make them lol.
I feel like I am getting close, but still not perfect. If I was able to figure out how to do hot foil embossing...then that would be perfection! But I have so many collectible books at this point, that there is not an end in sight anytime soon. I suppose if all of my books had a professional and official slipcase available from CD or the publishers, then I might opt to just buy those instead and save myself the time...as I did with Bill Hodges trilogy and The Fireman. But I doubt that all of the SK library will get official slipcases anytime soon.