Ugh. First, none of the bushings are "plastic". None of them. There are polyurethane bushings, polygraphite bushings, Delrin bushings, and of course the OE rubber bushings that I'm aware of. None of those are "plastic", and they all have different properties in regard to compressibility, durability, and elasticity. If you can't tell the difference between polyurethane and "plastic", you're probably not too well versed on their different properties either.
Second, I don't think you have a good idea of what torsional or compression forces are as they relate to the suspension. Because you don't want torsional resistance in any of your suspension bushings, it's a bad thing. Torsional resistance in the LCA bushings slows your suspensions response and keeps your suspension from moving freely. Same for the sway bars. And since polyurethane has higher a compression resistance than rubber by a long shot, I don't really understand at all what you're trying to say. The best case scenario at the sway bar bushings and the LCA bushings is the respective suspension parts moving without having the bushings resist or slow their movement. Now, harder bushings will transmit more suspension forces to the chassis and can add some harshness to the ride quality, but if your shocks and torsion bars are well matched that shouldn't be an issue. The softer the bushings are the more sluggish and vague the suspension response will be. And the rubber bushings are not more durable. They're more elastic, but they're softer, less resistance to cuts and tearing than the poly bushings are (just try and cut up a set of poly bushings!) That doesn't mean the poly bushings can't be damaged, but rubber bushings of the same shape would be damaged even faster. The strut rod bushings though are not the same shape, and you do have to consider the different properties of the different materials in those situations. Which I don't think is always done by the manufacturers, and why you get generic parts. Which is why I especially don't like the poly strut rod bushings that are out there, because they're generic for the whole A-body year range, which makes them the wrong size for at least half of the year range, if not everything...
