Hi Colin,
Personally I can think of better uses for £500 - extra tools, nice wood blanks etc.
I use the 5 preset speeds that you can change to suit your needs, Mine are set at 250, 500, 1000, 2000 and 3000. it doesn't take long to select one of those and then go up or down a bit with the relevant buttons. In fact most o the time, one of those presets works fine for the task in hand.
The one time I do 'tune' the speed is when turning large, out of balance stuff, where you need to get away from the harmonic speed, and reduce the vibration.