Re: Night Vision
Gen 1 is probably not worth messing with.
Gen 2, or at least the US mil spec gen 2 stuff will work alright with some ambient light, will be fine for citys, etc.
Now if you plan on doing hunting at night, killing hogs, etc, you pretty much need gen 3. Or go cheap and just buy a flash light. I would generalize that gen 2 has about half the spotting distance that gen 3 has.