#1: A network of radio scanners that can can be remotely controlled by the listener through the internet. Similar to the DX Tuners concept, but dedicated strictly to aviation and with scanning capability. A free for all system were anyone could tune anytime wouldn't work, so I envision a user pay system were you could buy block time and reserve the radio for your own use. You could keep the audio available to everyone, but sell the control. This way you could make some extra money to support the network, maybe even enough money so Dave could buy his own Learjet (think thousands of scanners worldwide).
#2: More radios dedicated to enroute centers (even if you can't hear the controllers).
#3: On exisiting radios at busy locations. Stop trying to scan so many busy frequencies at the same time. If you're going to monitor approach control at a busy airport the frequency is going to be active almost 100% of the time, so it's totally pointless trying to listen to tower/ground/clearance/enroute at the same time as well.
#4: Turn the frequency delay and priority functions OFF. Very annoying.
#5: Total worldwide global domination, a system that could that cover all ATC freqeuncies on the planet. After Dave makes billions, using idea #1 above, he can launch a few LiveATC.Net satellites that could be used to monitor all frequencies. (Bwahahahaha - Dr. Evil voice).
6#: Actually speaking of satellites, a receiver that could pick up SATCOM voice and CPDLC datalink communications would be cool.