OK, level editor == monumental && monumentally boring task. (@pedants: no, that doesn't parse meaningfully as a C++ expression, deal)
In an effort to make some meaningful progress, the Hacker Within has emerged and said those four most dreaded words (when coming from the Hacker Within): "Why don't you just..."
Sayeth the Hacker Within, "Since everything is specified in text files anyway, why do you actually want to make a UI? You've been editing attribute files by hand and it's fine. The file monitor already knows which file was used to define an object. When the text file changes, it auto-refreshes the object anyway. Why don't you just do a system call and edit the attribute file of the currently selected object in Notepad++?"
"Well, because that's a stupid idea! It's inelegant, hackish, brutish, and... oh, it's already done. I suppose it has that going for it."
"But what about..." I begin to protest.
Sayeth the Hacker Within, "Look, just make some buttons to copy attributes to the Windows clipboard if you want to edit something like, I don't know, transforms in-game."
This has got to be the worst best idea ever. At least it's progress.