Just so you know, the smallest imperfections telegraph through the new decals and can look pretty bad. The original screen printing has different thicknesses to the ink when it's applied, and even that can show up like a sore thumb though those new decals. It's best to strip the cabinet and sand it down, fill imperfections, prime it, then block sand it nice and flat, then put the new decals on. Putting decals on is a pain, but if you're gonna do it, might as well do it right. If you don't want to do all that, you might want to just pass the decals ahead with the machine like Vid said.
On a different note, you could airbrush the faded colors back into the art, like I did to the VFW pinball museum's IJ as shown on the video Clay has on the Pinball Ninja website. That's not incredibly difficult, and can actually be kinda fun, if you're into enjoying things that normal people don't find fun, and since you're asking about cabinet decals, you just might be that kind of person, LOL.