Minor races appear to be higher in tech almost immediatly
They always start out lower than me, but they can advance rapidly. Which is understandable considering that they only have the on planet to pay for, freeing up more of their taxes for research.
If you leave minor races alone for any period of time it will come back to haunt you
No, not really. They just usually sit there. Though in time they can end up with large ground forces to take out. A couple of troop fleets are usually sufficient though.
I left one minor race alone for too long and they almost became the power house of the galaxy, having to fight them back into submission and then take their worlds added years to my game.
Minor races don't expand unless someone gives them planets in exchange for techs. Nor do they have any ships other than scouts, constructors and orbital defenders. Which usually consist of un used freighters.
The minor races seem more amienable to trading techs initially compared to the other civs.
Yes, I find that to be the case. I can usually make better deals with them.
Does anyone know if you can do espionage with minor races?
No you can't. You get a message about not wasting spies on minor races.