AWS B5.1 outlines the expected capabilities of the associate welding inspector, welding inspector, and the senior welding inspector. It is expected that the senior welding inspector can and should be capable of writing welding procedures. That doesn't say the welding inspector can't write a WPS.

The is no document that I am aware of that states what qualifications are required to write WPSs. There are people in industry that write WPSs and have never taken the AWS CWI examination and still they function very nicely in that capacity. That being said, the training (or studying) one does in preparation for the CWI examination provides a fundamental understanding of what a WPS is and what it should consist of. Most codes and standards that involve welding include a sample form that provides some limited guidance about the (minimum) information the WPS and PQR should contain.

Still, there are enough subtleties in every code that a thorough understanding of their requirements are necessary to write a "good" WPS that is of any use to the welder. Many people that attempt to develop welding documentation haven't mastered the code to the point where all the requirements are met. Even the person tasked with reviewing the WPS has to have a good understanding of what is required and what is "good information" to include in the document. Everyone has their own idea of what should be included in the WPS and PQR. 

I suggest that you obtain a copy of AWS B2.1 and review the list of essential variables and then, with your welding experience in mind, include those things that you feel are necessary for the welder to understand what is expected of him. For instance, it is not required to record some of the electrical parameters such as voltage and amperage when welding up the test coupon, but you and I both know that it is important information for the welder to have when setting up for a new job that he or she may be unfamiliar with. The bottom line is, even if it isn't required information, it is useful information when it is time to write the WPS, so by all means, record it on the PQR.  The WPS should be complete enough that a welder can set up the equipment and the material to weld it and meet the requirements of the welding/fabrication standard.

Best regards - Al