Giving them one copper over one estate seems extremely silly: you're -1 coin, he's +1 coin after that if that copper hits a jack
Jack is a trasher. In some games, Jack is meh because you don't want the secondary benefit from Jack as silver. But that doesn't change the fact that Jack removes unwanted cards from your card via trashing. They are separate points and combining them only serves to confuse, not illuminate.
treating bandit camp as a necropolis with +3 attached falls into the classic F.DS mistake I see all the time: a large portion of the time your engine is not drawing your whole deck. Even if it is, it likely wasn't originally. Even if you were originally, the Spoils is put into your discard and the card you're drawing is still at the same proportions to be an engine card. So these obtuse analogies don't end up being that useful in practice.
I've been mulling over this response for a bit. I'd like to start by saying that I enjoy discussing all of the subtleties of Dominion and the many approaches to optimizing play, even where there is disagreement. And because there are many players with many levels of experience and ability, I almost always state my ideas and observations in the form of a question, explicitly asking others to weigh in.
In this case, my thoughts have been met with "silly," "confusing," "mistake" and "obtuse." It's hard not to be taken aback. I was simply trying to offer some other ways of thinking about cards.
When a relatively inexperienced user starts a thread with a question like this, I think it's important to try to help them expand their thinking. Most beginning users can play simple strategies, particularly BM. Learning all of the complex engine variations takes a lot more exploration and more patience and discipline, and learning to successfully evaluate a kingdom and decide on the appropriate path is incredibly difficult and subtle; too much emphasis placed on individual cards can create tunnel vision in less experienced players.
So, in the interest of clarity, I would like to revisit some of the points above in as non-confrontational a manner as I can muster.
I don't think I would use "+1 coin" as a description for someone giving you a Copper, no matter what the circumstance. Would you say that Mountebank gives you a coin?
You seemed to state that Jack is a trasher with Silver-gain as a secondary benefit? Jack only trashes some of the time and always gains a Silver. He seems more like a Silver gainer with occasional trashing/sifting as a secondary benefit. The trashing and Silver gain are not "separate points" because Jack isn't a thinner. His trashing/gaining has a very particular singular effect: To increase your average money density.
I did explicitly say "for deck drawing purposes" when talking about the pitfall of Bandit Camp. I'm not sure I would call it a mistake to strongly emphasize the importance of deck-drawing engines. They aren't just a little bit better than engines that only draw some of your deck. They're exponentially better. In fact, some players would say that if you're playing a bunch of actions but not drawing deck, it's not really an engine.
Again, that's something newer players have a hard time learning. Being patient and not just buying Provinces as soon as you start hitting $8 takes discipline. Seeing what happens when you can draw your whole deck reliably and plan out exactly what you're going to buy on every turn, not to mention make sure to always, every turn, play that exactly one copy of [insert attack card here] that you have in your deck. It's engines like that that make it so that when you see Ambassador and Jack in a same kingdom, you're almost always going to use the Ambassador if the engine is even remotely viable. Sure, Jack-BM might beat Ambassador-BM, but how often is that really the choice? Was it Stef who said don't play a 1-card kingdom? Or a 9-card kingdom? Or something?