Bob,
You said - “I’m pondering a modified-IPPW type layout, not up on benchwork fully, but solid, stable bench-work of about a foot or so high.”
When you stated your problem, I immediately thought of the same thing. Do you remember how Fred has those 2 foot by 2 foot patio squares that the legs sit on? I feel the key is the shear square foot age of the foot is what keeps things level. It all goes up and it all goes down.
Richard’s layout does almost the same thing, but does it by the rigidness of the benchwork that may allow any one leg to be lifted clear of the ground as the rest holds the massive benchwork level. So what if you don’t do the massive tear out and start over or chuck the whole routine thing, but repair where it needs to be repaired with a different solution? What if you took an area that was raised on your uprights and added another set of splines down next to the ground? If it is next to the ground bring it up 6 inches and put another set of splines. This would make the whole area from one upright to the next a solid box frame. Think of a trestle and even if you have to put angles, you are improving not just abondoning the idea. Do you have any areas that are not impacted? I would think, don’t touch except for the height transition to the new areas.
You know in the entire history of the Uintah Railroad, they had to have a steam shovel stationed at one area of the railroad for a mud slide, because it had to be cleared every year and sometimes many times a year.
This local knowledge of how to build is really the only solution and 50 yards or 50 miles can change everything. Good Luck, enjoy the challenge and try not to look at it with just frustration.
And I thought the “Ugh” was because we got to rowdy again. 
