I've seen some mining rooms which disprove your notion that GPU-only mining will stop the capitalised players having an advantage. They always will.

And yes, it's always a balancing act. The network adjusts the difficulty based on total hashrate, not on power efficiency, which is just an overhead. More and more people will pile in until the difficulty is high enough to render mining unviable. However, ASICs at least will shift the balance more towards hardware costs vs the raw power cost that it is now, and reduce the number of useless components that need to be manufactured, etc.