reason we don't see these fancy new things get to reality = cost prohibitive, bottom line.
I don't buy the whole "it destroys infrastructure so just shelf it" for superior technology because, those in power would have just casually introduced the disruptive technology at a higher cost and would have gradually introduced it to the upper echelons of society.
Cases in point = Moller international flying car, Optical Stealth by Susumu Tachi, and the JetLev.
None of those things exist with the exception of the JetLev and that is far from what we all originally wanted (something from the rocketeer - an actual, practical jetpack)
I will always call Bullshit on "free energy" stuff because a:
they always break the 2nd law of thermodynamics
there is always a catalyst of some sort that begins the chemical reaction that is NEVER considered/ ALWAYS ignored
because these products and innovations are "in theory" or "on paper" but never executed upon because of my first sentence. Why aren't there HUDs yet in average consumer grade automobiles? Why don't we have mag-lev enabled roadways yet with autonomous cars? (those could certainly be automated to provide both fuel efficiency and safety!)
I agree with you on the "free energy" bit usually being a bunch of crap. However, free energy isn't the same as scavenged energy, the system isn't perpetual because the source of the emission is constantly suffering decay as the particles containing the energy are released. This isn't a violation of the 2nd law of thermodynamics because sub-atomic particles have an intensive property of entropy. Solar power is an example of wasted energy until you convert it into something useful.
The end-cost is relative and is rarely a good representation for the actual cost...
I think the economic barriers to new technology are often the most prohibitive. The world is fueled by money, economic walls exist that serve to prevent technology from expanding too quickly. The investors like to see returns on their investments before pushing the next generation of tech; essentially pushing the old tech into obsolescence. Occasionally you have competing technologies from separate sources that will force a change but it's not a guarantee. Technology is growing too quickly; many new tech innovations are actually shelved until the "tap begins to run dry" so to speak. When that happens they unroll "the next big thing" and the profits come flowing in...
Also, the HUD thing is a good one. They put HUD's in some older Cadillacs, I think people were "distracted" by them. The mag-lev roadways with autonomous cars is entirely possible with consumer-grade tech but the fundamental resistance to change, lack of urgency, and high cost are all major road-blocks.
The Moller Sky Car was too much like an airplane yet significantly more expensive, and it didn't incorporate full manual flight control.
Optical Stealth is still promising...