I can think of a lot of older movies I'd not touch the pacing on. I don't think it'd improve the film. Then again, I admit I've bounced off a couple because of extremely-flat cinematography and slow-as-molasses pacing (the original Oceans Eleven comes to mind—I don't drop many movies that I start, but I'm not sure I even made it to the 20 minute mark on that one).
Maybe I'm misjudging what you mean by "old"—I'd kinda assumed you meant "before digital editing", say, 80s and earlier. I don't think films from the '70s tend to feel terribly different from modern ones (we've developed new and more-chaotic ways to assemble very bad action scenes, but that aside, not much different) for example, but would grant that it's probably possible to divide cinema into silent/middle/modern period as far as the feel or what's asked of the viewer, and that the former two do feel pretty different from modern films—but I'd say we were already transitioning out of "middle" and into "modern" in the '60s, so you've got to go pretty old to get into what I'd judge to be notably different.
Now, film films do tend to look very different from modern movies, even as recently as the 90s, but that's because easy digital color grading hadn't ruined the artform yet. :-)
