re: the Aquila Gambit approaches...
Nothing like reading it from the man himself:
http://www.bigear.org/vol1no1/clarke.htm
The concept put forth in this essay is not original, and the idea that we should look for the products of "astronomical engineering" has been perhaps best expounded by Freeman Dyson. But nowhere as concisely as by Stanley Schmidt in his novel "The Sins of the Fathers" (Berkeley 1976), which contains the chilling phrase: "Seyfert galaxies are industrial accidents."