Norval said:
3. Mankind was bioengineerd and destined to become their rulers / ambassadors of the Intergalactic Government. (Gives the reason for them having an interest in us.)
Not necessarily! Perhaps humans are farmed - an endangered population of once-widespread herding creatures. Perhaps, ground up, we are an alien aphrodisiac... perhaps we are tasty when sprinkled on food. Perhaps our skin makes the best kind of drums for alien rhythm bands.
Perhaps our sweat acts on aliens as a powerful hallucinogen, and they abduct us so that they can take big snorts of our armpit smell and stagger around bumping into things and saying "whoah".
Perhaps, like the Ilwrath from Star Control, the aliens like us because we have the distinction of being the funnest species to torture in the entire universe, and so we are kept around so that they can enjoy quality torture, instead of having to settle for cheap, unfulfilling torture.
Perhaps in their natural form, the aliens are armless, legless lumps, and farm us so that they can steal our limbs.
Perhaps human behaviour is naturally hilarious to all other intelligent forms of life, and we are exported to areas of the universe that are badly in need of comic relief.
All of these are unlikely...
... but not as unlikely as the idea that humans - who, as a group, can't run one planet - are being bred to be overlords to 57 varieties of alien.
I like the hallucinogen idea... of course, then it would be an interstellar drug war. I see nothing strange about that, if we're already accepting everything else on spec.