My $.02...
I have a customer who requires us to qualify our WPSs; that is to say, each WPS we use in production for that customer must be qualified. It's the most fun I have had in my job (as QA manager I don't often get to go play on the floor), planning, writing PQRs, witnessing the performance of the PQRs and seeing the results come back. Prior to my arrival here in April, all the welding was being performed with hastily conceived procedures, some of which had way too much information and many with too little. After a lot of reading (I am former Navy and the differences between Milspecs and AWS specs are many) I was able to arrive at the conclusion that any company that makes its bread by welding in more than one or two processes should go ahead and qualify their own WPSs. It will pay for itself with knowledge, as well as the confidence you will have in your processes.