Yes. But only if they are assembled from junkyard parts.
The tow vehicle was a 1964 body on a 1971 pan, the towed vehicle had a 36hp engine good for 40mpg with the stock aerodynamics. Everything is gone now except those Rader wheels.
Once a car has been on the road for 50-60 years it has conserved the embodied energy of three or four new cars. I'm sure the embodied energy is <25% of the rust-to-dust total. I have Plan B up on jackstands in a barn. It's a 1958 Beetle that's getting a Lexus LX400h electric rear axle. Right now I'm at the motor mounts and axles stage. Later comes the junkyard OEM inverters and batteries and chargers and .... the list goes on.
Your example Sparks and Micras don't sound all that old to me; but if they are
not electric then there's all sorts of opportunity to surpass 70MPGe. There are hybrid SUVs coming to market in 2017 that have a twin-motor electric-differential rear axle that will do torque vectoring.
The future is so bright we'll all need mirror-shades.
OTOH production of new (autonomous) vehicles will drop; but there's vast opportunity retrofitting the old self-driven fleet.