As @tiffle mentions, the Keyboard Maestro Brevis tries to address some of your points. I've been using it since I wrote it to handle 78 expansions of various types. None of them are in Keyboard Maestro's plist.
You're referring to the size of the plist. And I discuss this issue in the Brevis documentation. But the short version is that the Brevis expansions are all stored in one variable, which can be easily backed up, shared and restored using the Control Panel.
So the size of your plist isn't affected by your expansions.
In the years I've been using Brevis, I've very very rarely felt the need to edit an expansion so the Control Panel does not include that option. It's rare enough that deleting the problem expansion and redefining it (no matter how long or complicated) is easy.
That's in part because Peter wrote a macro to create an expansion from a selection that Brevis uses. So in Brevis you only have to select something, call up the Create From Selection macro, pick a typed string to call the expansion and a category to store it in (because it can be hard to remember these things) and you're done.
I'll add one thing Brevis does that I don't think the commercial products do. It allows either pasting or typing the expansion depending on how the expansion is initiated. This turns out to be very helpful in applications that struggle with the faster pasting (like InDesign).
Anyway, more in the documentation (including support for tokens).