This _could_ be another case of premature optimization, as gcc 4.9+ could automagically devirtualize non-overridden virtual functions. icc could do that for years.
That's not the way the phrase 'premature optimization' is usually used. Usually, it means spending time optimizing something that is not a limiting factor, or that otherwise will not make a difference in the final result. Keeping your code simple in the hope that eventually it will become fast is something else, probably falling closer to 'Sufficiently Smart Compiler' http://c2.com/cgi/wiki?SufficientlySmartCompiler.