Dick Harter was and is considered a coaching genius.
Harter, like Thibodeau is a good coach -- probably better than good --but the term 'coaching genius' in basketball is incredibly overused. Very good players make coaches geniuses. In fact in basketball as a whole, there has been very little innovation over the years. Most of the trends kind of evolve over time from coaches pulling ideas from what they see other teams doing.
Point being that talent wins, first and foremost and the best coaching in the world won't make you win with lousy talent.
Give Thibodeau last year's Celtics crew and they'd have still been the worst defensive team in the NBA.
That all being said, I would definitely pony up some extra cash to keep him here.