Well, if I was an enterprising and cunning alien,
I would hang around without revealing myself,
accomplishing certain goals:
1. Make sure they don't kill themselves off.
(I'd let them get close, though, so they learn a lesson)
2. Take extensive DNA samples of flora and fauna. Then when we make contact,
I'll trade them their own extinct species back for a pretty penny.
3. Discourage certain technologies I already know, so that the ones they develop to
compensate are unique ones, more valuable for trading. Then I steal them, obviously.
4. Record all their cultural emissions (TV, Radio, wireless Internet) for re-sale to
interstellar pirate networks - and to "Galaxy's Dumbest Home Videos".
5. When they finally develop interstellar spaceflight, in spite of my efforts, I'll make
"first contact", claiming some high and mighty "prime directive" kept me from interfering before >
