Regarding the post-alien-intervene-planet-earth's-economy, fruit for thought, think about this:
1. Did old John Bull "meant" for any good when they established "sovereignty" over north-american continent? I mean, was the economical system meant for any "greater-good" for the north american people? - you know they didn't "rob" you outright back then.
2. Do you really think we human can out-think those aliens who can space-warp and pest-control their target (planet earth), and device some economic system that based on our own way of business-conduct, while they, seems happy to "adapt"? - Credit economic system based on human society's credit of productivity?(non-raw-material-currency) "what the hell is that?" asked by aliens. You expecting cave-men got any good economic system to estabilsh with modern man?(cave-men still got some-what "economic system" works for them, and we are cave-men compares to aliens)
3. Further thought, maybe the SOLE reason the aliens didn't wipe us out once they made contact at first place, is potentially because they abey certain rules of their own moral (law) or rules of engagement (paramilitary expidition) or simply business contuct. -But don't naively think "they are here to help" (crapy movie "Red Dawn" anyne?) They freaking EXPLOIT "the weaks".
Slavery maybe illigal in their dictionay, but they may found psychos to testify on their "court", that these buch of creatures on planet Zeta-3 (earth) is not qualified for "conscious creature" or "intelligent creature" thus exampt from "slavery"...
"Destory" a habitable world maybe illigal, but they may change our eco-system and stand aside, wait for "Green peace" organization of their world to declare this planet(earth) is now considered non-habitable and then they move in, bring a "demolishing-redevelopment" team with them. The "CEO" of this "estern indian company" has long caculated this is far more cost-effective to re-terra-habitate a world, than "slaughter the indigenous, and face a heavy fine back home" kind of "investment".
Simply put, as "primative" as we modern human can be, we can manipulate the "humane standard" as F**K as what is nowadays the world can get - imagine blood thirst "opportunist", play around, in a galaxtic scale - for we, being play chips.
PS. Guys, what is the rareist material of the galaxy? H3? U235? Liquid water? my ass! THE most rareist material in galaxy, is Bio-mass. Being biological, is THE most rareist thing.
So, I vote, for "the most likely alien", being the zerg alike or tyrainy (help to spell? anyone?) alike or "the reapers" alike, bio-consuming aliens. The so call civilized community of protoss alike, eldar alike or galaxtical council alike, don't stand a chance.