I do low power embedded stuff, but have a friend who used to work on power management for linux for a uP company. I think we'd both agree that the only way you end up with a low resource system is is power and resource consumption has to be go/nogo test that management enforces ruthlessly[1]. Otherwise what you end up with is a pig.
[1] As in
Developer: this module works!
QA: Power usage went up 5%, rejected.
Developer: runs crying to management
Management: Fix or be fired.