Finally ordered a set of Scott's rear spring replacements. Took about an hour to install in icy rain - 50 minutes for getting the car jacked up, tools as needed, and the first side finished, then 10 for the second. It's a pain that the Insight doesn't have a front or rear mid jack point.
Initial impression: this really is how the car should have shipped from the factory. I'd say the front is still a hair more firm than the rear with the new springs, which isn't bad, but I guess I was expecting it to stiffen up more than it did. It's more like, just on the soft side of "just right". I could probably go a hair stiffer. Body roll is reduced tremendously and since the rear still isn't as firm as the front, it didn't noticeably add any harshness over small irregularities.
Pic is of the old springs, the new ones look about the same, just a tiny bit thicker and less dirty.