The 3/4" plywood used in the vintage JBLs probably did vibrate, but in a way that was pleasant to the ear. For me, I am not particularly partial to speakers with heavy cabinets, but that's probably more to do with the overall design than the cabinet per-se.
How thick should the front baffle of speakers be?
Some manufactures advertise or hype a thick front baffle, two layers of MDF, if the woofer is as thin as paper cone how could it change anything. Could be just hype