I totally agree. I too pick and choose my battles and I would definitely fight this one. I would not go through all of the hassle of revising all of my documents if I didn't think it benefited the user(s) - that's probably why there isn't a shall in the standard, who benefits from this?
On a side note, AS9100 and FAA requirements soon to be applicable to us do require this (Quote: AS9100 4.2.2b - when referencing the documented procedures, the relationship between the requirements of this International Standard and the documented procedures shall be clearly shown) - so even though I think this benefits the auditor, not the user of the document - I'm creating a matrix. THERE IS A SHALL!
Other people use their document numbering system to show relation to the element or clause, though I've never been fond of this method because standards are restructured and element/clause numbering revised, some procedures/processes fall under numerous elements, etc. In our particular case, I'm creating a matrix because we will be compliant with and need to show the relationship to numerous standards and regulations.
Just some thoughts.