I'm with ForceFlow on this one. I used to think all original was the way to go, but I'm such an anal freak about my machines that looking at fade or scratches or any type of flaw for that matter began to bug the shit out of me. When I restore a pin now, I want it looking as brand new as possible, and to do that you have to replace parts, decals, etc.
But I'm NOT a fan or repro circuit boards, and will always sell the repro to get an original. The serial numbers can be matched with new labels during the restoration, so that's not a biggie for me.
Keep in mind (and pardon the car comparison) that most antique cars have repro parts somewhere inside them to keep them going and looking new. Pinball is no different. (I'm also not a fan of that smoky disgusting smell most old pins have...)