Basement: 2.35m Ground floor & upper floor: 2.50m Higher was not worth a cent more to us. In houses with ceilings that are too high, it somehow creates an office-floor feeling for my taste...
But I wouldn't do it just because of the spots. The increase costs you 3,000€ and removing a floor costs a similar amount. You could buy many built-in pots for that, even if you have to pay the horror prices for prefabricated ceilings. Because as you say, spots are for ambiance or specific effects and not for illuminating large areas.