If the height of what you have now is comfortable to use and you like that height, get the same height cabinets in your new modern look. If you want higher cabinets, ask your kitchen designer to find a place for a folding step stool, perhaps in the pantry.

There is no need to decorate above the cabinets. A key part of the sleek look is to have nothing on the walls to interrupt the smooth surfaces. Glass-fronted cabinets above the main cabinets are good for museum-style display when their interior lights are on. They aren't shown much with contemporary looking cabinets.