This affect could be multiplied by the work being done at CalTech by Dr. Julia Greer and her Architectured Materials Team.

http://www.jrgreer.caltech.edu/home.php

They are producing nano-structured trusses that have hollow truss members a few microns long and a few nanometers thick, with strength equal to an equivalent volume of solid metal, or of Sapphire (Al2O8, IIRC). They are now reporting 100/1 ratios with equivalent solids. Note that members small enough to have few to no crystal imperfections can exhibit not only greater strength per kilo of mass, but in the case of Sapphire, the truss can be compressed up to 50%, and it returns to its former shape after compression is removed. Not only would this make for incredibly low mass spaceships but it can magnify the number of projects doable with the mass obtained from Earth’s temporary moons.

Start a lunar surface base, with landers built at EML-1 from “temporary moon” material, using these nano-structured trusses, and you would still have enough mass to start building the equipment for harvesting farther Near Earth Asteroids. You might even have enough to start a base on the surface of Mar’s moon, Phobos, which could start doing the same things there, including landers for Mars. If those asteroid flyby rates are high enough for these smaller objects that have a low enough delta-v to be captured for an average of 10 months, then they might provide a far less capital intensive bootstrap into harvesting asteroids and settling the Solar System.