Right, warning free code is a good idea.
Nevertheless one should specify Boost include path via -isystem path/to/boost and not via -I path/to/boost if one doesn't want to see the warnings in system libraries with gcc.
That's a bit like putting black tape over a "check-engine" light. My primary question still is: What is the disadvantage of adding the virtual destructors? The Stroustrup book has a very clear recommendation (below). Why not follow this advice? I'm keen to learn the facts. Ralf Stroustrup 2000 Section 12.4.2 (page 319 in my edition): Many classes require some form of cleanup for an object before it goes away. Since the abstract class lval_box cannot know if a derived class requires such cleanup, it must assume that it does require some. We ensure proper cleanup by defining a virtual destructor lval_box::~lval_box() in the base and overriding it suitably in derived classes. ... ... We have no way of knowing exactly to which class the object pointed to by p belongs, but thanks to lval_box's virtual destructor, proper cleanup as (optionally) defined by that class' destructor will be called.