There are some other things have come to light over the years about the Cacti code base. We realize that it can be quite a task to figure it out and efforts are underway to improve the readability and organization of the code base. These efforts aren't only for the Cacti group but to help everyone out there hacking on Cacti. We want to encourage people to get involved in the coding of Cacti and contribute their ideas and energy to the project.
Not sure how it would work but apart from internal documentation (and some kind of high-level philosophy of the "cacti way"), if you really want to get others to work on the code, I think you need to be more transparent about the development somehow. I know I gave up on a few things I wanted to add because I got the impression that while I was working on code, loads of things were going on in the background and the code I was working against would just take a sharp turn any second.
Good to hear things are still moving though! :-)