I'm a playfield swap guy too.
Picked up an EK hardtop at expo a few years ago and ended up selling it for a loss to get a CPR repro. They just seem to have a plastic, glossy look to them and to me they do play differently. And if I tried one and didn't line it up properly it would drive me crazy.
Not only that, but it's nice having the underside of the pf all clean too - if you hardtop you COULD pull everything off the bottom and sand it, but by that time you might as well just replace the pf.