This was exactly the problem I had since CEP 2.0. I'm currently creating a tool that generates placeable blueprints from a CSV table. It's designed to make editing a large number of blueprints as simple as possible. I'm almost finished, but need some time for testing so that the tools is reliable. Maybe such an application could help you.
Higher Ground had such a tool, because the HG builder's module contains an obviously generated list of placeables, but it wasn't released to the public. Maybe it was a script too limited for general use.
Placeables are quite simple to define, and the tool can easily to be enhanced to support door blueprints as well. Creatures are the most difficult. Due to the sheer number of creature abilities, one cannot maintain them efficiently in a list. Maybe the tool could offer the builder to define the class levels and the level-up package to use. However, one has to implement an interpreter of level-up packages.
Concerning items, I don't know which item blueprints should be offered and how to organize them systematically.
What is more, one could re-organize the placeable palette to fit the new models offered. I've already created a tool that can generate a palette, too, in an easier way than GFF editor.