In the industry the instructions are written for professionals period. Elk happens to be one of the few (if only) mfg that actively supports the DIY market.
I have read the ELK manual many many many times and I still dont know all of the features by heart (not even close). The reasons for this are that they have a very feature heavy system, they have certian information required by UL, ULC, ANSI SIA, NEC, CEC, NFPA, and the FCC to a very small degree, and they are trying to have a one size fits all (professional and DIY installers) manual. All of this is my opinion btw.
There are capabilities that are not even described in detail since it would probably add dozens of more pages. They give you enough information to get up and running plus all of the required information for the different regulatory agencies From there you can use the RP and run with it. Wait till you have used it for a month or so and you will really love it.
I have read installation manuals from Ademco, Napco, GE, Visonic, Electronics Line, and several others as well as the ELK and I feel that the ELK is pretty well laid out and very clear (all things considered). Having worked with many different mfg's over the years I can say that they all take a different approach to their "style" of manuals etc. None are perfect. Having set up and extensively tested dozens of different model systems I still had questions on the ELK system since they are a little different then other mfg's in their design (hardware and firmware). Once I caught on to the approach they took it became fairly easy to figure out how to do about anything I wanted.
The fact that you were able to install your system and get it up and running (with help from here) seems to indicate that they did a pretty good job. Since most systems are sold to professionals who would not want as much detail I think they had to draw the line somewhere.
I think that is why Spanky hangs out on here. He seems to love to help people (even if its not an ELK specific question). I have spoken with him many times and hes a hell of a nice guy (time to send another check Dave).
Good luck and have fun writing a DIY approach to the installation. I am sure that many people would love to see it and I would bet you will be a major help to others.