I went and checked a couple tickets after reading all this, actually didn't find foul play:

United reservation - exactly 85% of base fare quoted to me on the 15% discount, with taxes held equal. Is it supposed to be 85% of the total fare?

Virgin America companion - VA receipt was strange with a base fare quoted of 0 pts, $87 taxes and 850 total. Really weird, was charged around 500 and when subtracting 87*2 I ended up at the base fare quoted by Spirit. So I think it's all good, though really weird that Virgin almost was considering it a reward redemption. Still saved 350 for the pair of us to go to Vegas, so I'm not very upset!