Thanks to everyone for their perspectives. The Physics Man thread from a number of years ago was terrific, he is much better at understanding the mechanics than I.
I've ruled out the VIST plate system and will be getting a Griffon, Squire, PX12 Jib, Knee or STH based on what I can find in terms of deals. But in doing the research, my husband had a conversation with the US VIST distributor, who is at Stratton, who was pushing as advantages two factors that seem applicable to mounting a flat binding:
1- binding ramp (delta) angle - "Mr. Vist" indicated that a zero binding ramp or delta angle would improve the stance on a wide softer ski. I know that in addition to adding a lifter to the front of the Vist system, you can add a comparable spacer to pretty much any binding. I saw on the Knee Binding web site that they have a default 6 degree ramp angle but sell lifters to eliminate some or all of that forward lean. My boots (Doberman Aggressor 100) also have some ramp angle which would add to whatever the binding has. So my question is: is a zero (or reduced) ramp angle beneficial for this type of ski which would be used in new snow, spring conditions?
2- fore/aft mounting - The second advantage touted by Mr. Vist was the ability to tweak the fore aft position, an advantage not available without going to a more elaborate binding system. This raised in my mind the question of where to mount the bindings. I would typically, per conventional Jeanie Thoren thinking for women, have the bindings put a little forward. Is this still a good idea - I don't expect to have access to the Campbell Balancing system that has been written about here.
Those would be two very good reasons to go with that system. But only if you actually need to make those changes, and only if you can do that without paralyzing yourself (never happens on EpicSki). Having the correct binding delta can make a profound difference on your skiing. If you are happy with the way that you stand on your skis now however, you could just measure the delta on your current bindings and get something that is the same. If you've been struggling with burning quads or something like that, it could be really good for you because it is so easy to experiment with ramp on a plated ski (I think the VIST binding is the most convenient for this, but also limited in how much adjustment it allows).