The big surprises here for me are:
Masterpiece, Develop, and Loan so low.
Sage, Oasis, and Bonfire so high.
Masterpiece: So, you're playing big money or a Duke/Silk Road rush. You have 7 coins (or 8+ coins early, or 5-6 coins in a Duke/Silk Road rush). What to do...? Overbuy Masterpiece and be very happy! It's a pretty limited card, but when Silver is what you want, Masterpiece hits the spot.
Develop: Tricky to use, for sure. It has a lot of potential in the right kingdom and in tandem with limited gainers (often Silver/Gold gainers). Even at its worst (well, ignoring Poor House), it's a decent Estate trasher. Top-decking the gained card(s) can be a big tempo advantage.
Loan: In treasure-less decks, it's like a Junk Dealer that can only trash Coppers. Junk Dealer is amazing, and so is Loan - in decks where you don't plan to buy or gain additional treasures. Loan becomes frustrating the moment you add a single treasure you don't want to trash, but it can still have some value if you plan to add treasures late. I find that treasure-less decks are more and more common as expansions are added, so I look more fondly on Loan.
Sage: Maybe I don't know the right time to get this card, but I've been disappointed every time I've bought it. Sure, you can find your other opening buy easier. So it sounds like it might be good with something like Sea Hag or Young Witch, but you really need economy with those cards. Maybe it's decent with Militia or Cutpurse? I dunno. Later in the game (especially with trashing) it approaches a cantrip. Once you start greening, the filtering is much worse than Farming Village. And you don't want multiples of Sage. It's SO low-impact. It's the Pearl Diver of three coin cards, in my mind.
Oasis: This is a pretty lackluster card. Sure, if you have only one or two and haven't trashed heavily, it's as good as a Peddler (and better in unusual circumstances). But Peddler is a card I want to have a bunch of. I don't get excited about one or two. Caravan Guard is bad, but Oasis is worse, IMO.
Bonfire: Limited copper-trashing with no benefit. You want to use this early in the game, otherwise you're likely to have treasures you don't want to trash and/or more than 3 coins. But you really need more cards early in the game to improve the quality of your deck. I'm not impressed. Maybe Bonfire is more valuable when paired with a decent Estate trasher that also gains non-treasures (Remodel, Transmogrify, Develop)? I guess you can trash Ruins, too. Meh.