I'd just throw into the equation that Torres, the father of the Spanish guitar, built a guitar in the 1880s with a papier mache body to illustrate the importance of the top's contribution to the overall sound. It still exists, but it's too fragile to play. That's the first example I know of a guitar with a "composite wood" body, so it's hardly a new concept.
I don't think it is true to say that these guitars won't improve with age, if the tops are solid. It is true to say that a spruce top will improve more with age than a cedar top.