Sure, all of those Solar System diagrams could be declared obsolete (like so many political maps of Earth have been), and we could retrain ourselves to think of eight planets, plus the traditional Asteroid Belt between Mars and Jupiter.

But I don't think we should. I think Raoul's point is a good one: We teach science to children stepwise. We don't start them in physics with quarks, gluons and General Relativity, nor do we start them in astronomy with Chandrasekhar limits, Schwartzchild radii, and the carbon-carbon cycle. When they're older, we can bring up the idea that Clyde Tombaugh may have not discovered the Ninth Planet but the First KBO... meanwhile, I don't find it 'unnatural' to Science to honor tradition.

As an aside... I was reading something the other day which reminded me that when I was little and first falling in love with astronomy, the jury was still out on the origin of lunar craters: impacts, or volcanic? Seems incredible now - but did the eventual knowledge change anything about lunar nomenclature? Mars has a hell of a lot more features than Sciaparelli and Lowell saw - did we throw out their romantic, classical names?