Your point there sums it up Col, if your monitor shows you a picture that is spot on to the scene you saw and then also the prints come out the same as your monitor shows there is little need to play any further.
Where the calibrators do work best is when people are having a hard time getting all the colours lined up between the original scene, the monitor and then the printer.
I know in our case that once the calibrator was bought and used all the prints come back from the printers looking the same as the screen and regular use keeps them that way.