I don't think that any of the developers in the project have looked at the extracted documentation more than once.

I think it's totally irrelevant if they looked at the extracted documentation or not - the question is if they looked at it all. If they read it inline in the source code you just wasted one run of your extraction script.

If they didn't look at it at all, you'd better spend your time with writing tests instead of documentation. Tests also document things in a way, and are more valuable if your colleagues don't look at the docs.

BTW I was a bit confused, because you seem to be talking about code that is neither visible to a customer (through an API or a command line interface), nor regarded as "re-usable", because after your own logic, code has to be documented if it meets either of these two criteria. If you have large amounts of code meeting none of these criteria, chances are that documentation isn't your biggest problem at all.