I've got a new idea for a formula of racing. Why not specify in the rules "the car itself may act as a wing, but no external wings or downforce elements are allowed".
This means you would have ground effect and all that, but the lack of other wings would restrict downforce to reasonable levels. More realistic for road cars as well - who has little winglets coming off their car everywhere?
Of course, there would probably be a bit of ambiguity about what is and isn't a downforce element...