I see a couple of camps in thsi debate -
How about someone wanting to be a citizen "adopts" 128m^2 of the public space, limited by the amount of public space on offer. They would not have the right ot build on it - though they would be financing the land plots in the public area. This would accomplish 2 things:
1. Finacially, larger public spaces would be economic - and posisbly used a bit more!
2. People would effectively "own" in trust anyway, CDS
3. Limits the # of citizens by the plots.
I know a lot of details need to be worked out - but this looks like a possible compromise?
(I thought of this when a local public radio station is tryin got buy a new transmitter and is doing an "adopt a watt" campaign)