Mining Road could be used as a sort of Copper version of Desperation - gain an extra $1 at the cost of adding a Copper to your deck. But of course, it would be especially strong with gainers. It would also effectively work as a discount on Treasure cards (albeit on only one Treasure card per Mining Road you've played). Buy a Gold for $6, play it for +$3, and it's like buying a Gold for $3 (... Mining Road + Highway would be a good combo here - with 3 Highways that Gold is effectively free, and with more than 3 Highways, you're netting +coins). Mining Road + Tools seems like it could be really overpowered, since Tools can gain a Treasure card you played before it, and Mining Road would let you immediately play that card (imagine that combo in a game with Platinum!).
Tools in general seems potentially overpowered. It's like a much stronger version of Changeling, since you don't have to trash it to gain, and it can even gain a Duration card that someone else has in play (or Reaction cards that go into play like Sheepdog). The only place where Changeling is stronger is that Tools can't gain non-Duration Night cards and the lack of Changeling's exchange mechanism, but neither of those is relevant in a lot of games. So in general, it's going to play like a stronger Changeling. It's gonna be really strong with expensive cards like King's Court or Grand Market with its Copper restriction. It'll be interesting to see how it plays out in practice, since the fact that it made it through playtesting suggests that it's not as busted as it appears at first glance
Rope looks pretty strong, especially in games with junking attacks (although limited by the fact that you can only trash from your starting hand each turn), but even after you've trashed all your junk, the duration draw would still be useful, comparable in a way to Supplies which is also a Copper on-play that nets an extra +1 Card in your next hand
One interesting use of Prepare that I can see is that if you'll be reshuffling for your next hand, you could use it to keep any Victory cards in your hand out of the shuffle (potential Scout combo here!) - of course, that'll normally only work if you have 4 or fewer cards in your deck at the end of your turn (duration draw or things like an opponent's Council Room could let it work with more than that of course), so for it to work consistently, you'd need a strong deck-drawing engine - but in kingdoms that favor such engines, it'll be very strong! It could also serve as a counter to Haunted Woods - buy it first and you'll have nothing in your hand when Haunted Woods' attack is triggered. One downside is that Prepare would clash with Night cards - you can only buy Prepare before you get the chance to play any Night cards, and those Night cards won't get played at the start of your next turn (with the obvious exception of Werewolf, which would be played for the +3 cards at the start of turn), but games with both Prepare and Night cards aren't going to come up that often, so that's a fairly minor downside
It's interesting that Malestrom doesn't have an "if you did" clause. You could potentially use it as a pure Attack without trashing any of your cards, although that potential is limited by not knowing (in most cases) whether your opponent will benefit or hurt from trashing a card in their hand. I'm wondering if a version was tested that either had an "if you did" clause or had "may trash" for your opponents