So here’s a view of the same corner, with my “blend against every nearby region, not just the ones sharing an edge” fix in place.  As you can see, everything is much smoother!

Unfortunately, it’s also much slower to calculate the initial list of nearby neighbor regions;  it takes about half a minute for the game to start up due to all the calculations.  (By comparison, in the earlier screenshot, it took only a second or two);  I’m going to need to put in some more smarts, to make it a bit less ludicrously slow.

And here’s the same corner again, with regular grassy terrain and non-flat-surfaces turned back on: