The 1920s British light aircraft competitions at Lympne led to some interesting machines, but draconian engine displacement restrictions and other criteria meant that most machines created for the competitions were impractically light, expensive and underpowered. Those that did see some measure of post-contest success were generally up-engined and strengthened in their production versions (de Havilland Hummingbird, Westland Widgeon, Blackburn Bluebird, Avro Avian) and none were as successful as the de Havilland Moth, which focused more on being cheap than on being especially light.
What if EAA were to create a competition to encourage the development of new designs? It could take place, for example, at an airport near Oshkosh the week before Airventure, displaying the planes at the fly-in and maybe saving the last competition event--a speed race, for example--for the week of Airventure. What class of aircraft would you like to see compete: ultralight, light sport, general aviation? Single- or two-seat? How would you handle engines--displacement, horsepower, identical models? And what criteria would you like to see used for scoring? Maximum speed? Minimum speed? Take-off and landing distances? Rate of climb? Fuel efficiency? Gross weight over empty weight? Handling? Cost? Ease of construction?
PS--If I won the lottery, I'd use it to fund the development of a couple of relatively inexpensive, four-stroke aircraft engine, say one in the 40-50 hp range and another in the 80-100 hp range. I'd then put up the money for a contest like this, for planes flying with those engines, with prizes for the winners and even a small stipend (say $1,000) for any plane that completed the competition. That's the kind of thing that would generate a lot of new designs, press interest, and help to jump start sport aviation. Of course, I suppose I should start buying lottery tickets from time to time.... ;-)