Jeff,
This is a problem we all have to wrestle with from time to time.  All a matter of client education.  I don't know of any short and sweet text that addresses it but I'll throw out what I usually tell them....

Building Codes evolve from necessity and experience.  The codes are presented as minimum requirements necessary to protect the health, safety, and welfare of the public, and yes, it is "one size fits all".  Because a building has been performing adequately for 30 years does not mean it would perform adequately if subject even to its own design criteria.  It usually only means that the building has not been subjected to its design limits.  Fortunately, most buildings are never subjected to these limits and we should be thankful for that.  If our buildings, given the current state of construction, were continually subjected to their design limits, we would likely see lots of failures.

The second thing we have to consider is that, as engineers, we are licensed to protect the health, safety, and welfare of the public.  This is not true of building owners, developers, or contractors.  Our duty to the public is greater, and thus our liability for breach of this duty is higher.  We must, therefore, yield to our Standard of Care, which is that we must use the same level of care in our practice that reasonable professionals practicing in the area under the same or similar conditions would use.  This simply means that we must use reasonable care in our practice and to subvert the evolution of the code process by not informing the owner that we have a duty to comply is a violation of our ethics and our laws of practice.

The third issue, and the one that usually gets an owner's attention, is that our professional liability does not cover us if we willfully breach our standard of care.

None of this prevents us from being innovative.  Innovation occurs when there is no other valid limitation or guideline behind which we can be adjudged negligent if the result is a failure.  Accepting a structure without assessing its compliance with reasonable standards and offering solutions and attempts to meet these evolve criteria, does not constitute innovation.  It often constitutes negligence.

Tremendous Ron!  I am printing that response out now so as to reference later and to pass along to all young engineers.

Thanks for taking the time to share a well thought out address to a complex question yet one so commonplace.

Thanks Q...I occasionally have a lucid moment!