Vinyl cote sprays smooth as glass.. it's really made just for coating vinyl surfaces. Although even tho it's a great product for what it does, I can't really quite gather *why* you'd spray it on silkscreened arcade art. Not necessary.
Frog juice i'm also familiar with, but it's just a UV protectant of sorts, not a really long term durable coating. Lots of sign folks use it to help with the colorfastness of their prints in outdoor applications.