I have now had a plethora of instances where hours of work has produced a site/template/page that looks identical to the starting point and no one can tell I was there. But, to my credit, the way the site/template/page works is sometimes entirely different and at the very least is more standards compliant than the original. It sometimes takes a lot to convince people that they need to do this type of maintenance or change because they see only the "surface". That said, the search returns and general functionality at the end of the transformation is proof enough that it was all worth it.
In as much I as I always try to push a little for upgraded design, I don't mind having projects that don't change appearance but change functionally. It is a project for my pocket, it improves the site tremendously, and access is more important than the fact that I might have really wanted to get rid of the blinking marquee that the client loves....