Servicing low-density suburbs is very expensive - all that asphalt and pipe for relatively few people per hectare.  Now if you could design new suburbs to be more self-reliant in terms of wastewater treatment, water supply and energy supply - net-zero energy buildings, stormwater utilization, permeable pavement, etc. -then that could alleviate some of these costs. However, you still have the issue of car-dependency requiring wide arterial roads (aka traffic sewers)