GPU's are still getting 60-100% performance gains every 24 months. GK110 is twice as fast as gtx580, and even if you think that is an unfair comparison somehow, gtx680 is still 35% faster than the significantly larger and more power hungry gtx580.
There was a big shift by Nvidia to concentrate on performance per watt after Fermi. They're still going to concentrate on that metric, but since the shift has already occurred the performance penalty has already been suffered. Nvidia already has a much more efficient design to build off moving from Kepler to Maxwell, so sacrificing performance to achieve a better perf/watt metric will be easier to avoid. Maxwell will likely have it's ~300mm^2 die as it's flagship Geforce chip for quite awhile just as Kepler did, but it's also going to be 70-80% faster than GK104 (just like GK104 was over GF114), so we'll have a $500-600 solution 20% faster than Titan by ~Q2 of next year.
I don't see how any of what you said justifies the doubling of price brackets for each performance level.
With CPU's Intel have lowered the ceiling in an effort to make the floor look more appealing, thus people are happier to pay $200-350 for a mainstream chip because it has same image a $500-600 chip had pre-2010.
Nvidia on the other hand have mimicked AMD's R700 approach
without also lowering prices accordingly. Of course, this was possible for NV because AMD failed to deliver on performance, so they are almost as much to blame. At least now their prices are a bit more in line with past practises.
Like Intel, however, NV have repacked a 'server' chip for consumers to retain their high end, but now have a mantra of low urgency on releasing such chips. As such they will likely now overlap generations. I do not think that Maxwell GTX780 will overtake Titan myself, and Titan will remain valid on a very small scale until the next, Maxwell-based iteration of it is released - a year after GXT780. Sound familiar?
EDIT: With that said, I want to add that I understand the shifting market. My next build will be mATX, and possibly even an ITX system to supplement it. I don't see how my yearning for a proper high end would suggest that I should just buy a console and be done with it, quite the contrary. Regardless of this view, I am someone who buys in the upper end of the sweet spot, so the strategy of efficiency does cater to me - the high asking prices being coupled with it does not.
