I printed labels with solvent inks for years. That really degraded my squeegie edges fast, so sharpening was absolutely necessary (otherwise I would have been replacing them way to frequently). Sand paper produces a much rougher finish and allowed the solvent to attack the blade faster. I bought a basic sharpening kit from Encore and the diamond cutter heads produce a nice smooth even finish if you progress in small steps and finish with the smoother diamond cutter. Really helped when printing solvent inks.
Speed is important as is how much you try to remove at a time. While I have a motor that was made to turn at a lower rpm than a router there is no reason that you couldn't use one. All good woodworking supply stores like Rockler sell variable speed controllers that make it easy to run a lower speed without modifying your router.
Plastisol and wb just don't eat my squeegies like the solvent based inks did, but it sure is nice to take a pass on my blades occasionaly, particularly if I get nicks or edge damage of any type.