Yes, but that's not necessarily crucial. It's indeed glorified recycling if it takes a barrel of oil to make a pile of garbage from which we can then extract a half-barrel of oil. But if it takes a barrel of oil and a whole bunch of sunlight to make a pile of garbage from which we can extract two barrels of oil, we could well be ahead on the deal. The key equation isn't total energy in the system versus total energy out, but energy we had to add to the system versus total energy out.

This is the problem with the example. What if the boat were made of wood? You might get back your 50 gallons, or even more.

Thermodynamics tells us that the gain, if any, will be much less than the energy that made the crap in the first place.

Quite true, but as the financial folks like to say, "sunk costs don't count".  The materials were put into the demolition debris years to decades ago.  Nothing is going to reduce the energy which went into them; the only question is, what useful outputs can we derive?

Landfilling yields zero immediate output, and is quite GHG-positive after allowing for methane leakage.  Gasification not only eliminates the methane and the need for the landfill, it can be sited close to the source to minimize energy costs and emissions from transportation.  On top of this, it reclaims metals and yields non-leachable aggregate-quality slag which can be recycled as new building material.

It probably makes sense to reduce the high-energy materials (wood, plastic and whatnot) which go into construction.  But nothing we do today is going to change what was used in the past, and it's the historical construction materials which determine what kind of demolition fuel stream we've got.  If that stream will become mostly inert 30 years from now, it doesn't change what is sensible today.

(FYI:  I'm short with Cherenkov because his objections are barely above crank-quality.)