If you build it, they will come...
I went down the same path, and decided I am far too unambitious to expend that sort of effort. I would certainly be a very happy 'consumer' of your Index if you decide to build it.
Even a simpler 'Master Index' than you describe with just the main heading for each PDF file would add substantial value over the current design. Of course, sucking in all of those 'subheadings' would be even better...
3 cheers for realneal!
1986 300E 5-Speed 240k mi.