I love these stats. One of the more interesting things that I have noticed is when not to buy the really good cards.
When I sort by win% for when "opponent only gains" most of the cards on that list are good cards. I have a 100% winrate when only my opponent gains forager, plaza, menagerie, chapel, mountebank, herald, cultist, wishing well, squire, remodel, upgrade, city, university, hamlet, jester, ambassador, and urchin (plus some others like thief). These games don't make up a huge percentage of my overall games (4 mountebank games, 4 cultist games, 7 city games, etc.) but it is interesting to look at the importance of recognizing when it is unnecessary to buy those cards where more inexperienced players might see a card and immediately get it without thinking (guilty of doing that as well).