rod: What do you mean about not being able to buy a Village? I don't know why that would be bad.
But yeah, you almost certainly avoid +Buys. You also never ever ever buy Treasure Map! You probably wouldn't buy Baron, either, even if it didn't have its +Buy. I'm sure there are still some good engines, though, like Village/Torturer and Minion. But a lot of engines really need +Buy, and those are just too risky.
Unless you can somehow build the engine first and throw in a source of +Buy at the last minute before it starts firing reliably. Like maybe you build Village/Conspirator and only throw in a Market once it's going. That engine needs some trashing, though, and you have to be careful there. Chapel and Steward are okay. Trading Post and Remake are not. You pretty much never buy any mandatory trashing cards, although the one you mention -- Lookout -- is one of the least harmful of those.
For a few strategies, Copper is okay. Horse Traders/Duke, for example, would be perfectly fine, because you want to pick up Coppers whenever you can.