Okay, there are basically three (mechanical) things here, and I want to touch on them all. 1)Coin tokens, generally; B)The set-up clause; 3-and/or-C - oh let's just call it III) the card itself.
Coin tokens: Seems to me these are best in... engines. I see a lot of engine hate out there, but in principle, what kind of deck underspends more often than others - typically engines. Engines also tend to have the +buy that can take best advantage of the tokens in the endgame. Moreover, they will reasonably often be able to cobble up extra engine pieces essentially out of nothing, with the buy. On the other hand, they're actually *great* for slogs, where you really spend exactly basically all the time, and smooth 4s and 5s are great. Of course, that's hypothetical, and not knowing how exactly you'll be able to get them, it might be very hard to get slog card and coin-giving card.
I think spoils are a reasonable comparison in a number of ways. Of course, I actually think these things might be better for engines than spoils (well, okay, I will usually take a spoils over a coin token, granted, as it's worth so much more. But I expect that, for engines at least, I'd rather have 2 coin tokens than a spoils) because they don't take up space in your deck. That is MASSIVE for engines. But okay, I also think spoils are probably misplayed a good bit, and these will be, too. You really have to time spending these things right. The impulse is basically always going to be to spend them right away, nownownow. And yeah, usually, that's probably going to be right. But I expect tere will be a lot of exceptions (and this is why I am throwing the spoils in), even when spending it WOULD let you buy something better for your deck. Sure, often (say you're playing BM) you'd buy province on $8 on turn 5, but you almost certainly shouldn't spend 2 coin tokens to do this when you could buy gold and keep them, and actually I'm quite sure you shouldn't even spend 1. Well, these may be obvious examples, but I'm sure there are lots more that are, generally, much more subtle.
But okay, what can we expect to see? Can't really have a village that gives them, as barring black market, it's strictly better than bazaar if it costs $5, and at $6... well, you'd need some other ability. Necropolis which gives you a token could be a $2, probably reasonably balanced, not terribly hot. I think more interesting would be something like "+1 buy. Gain 2 coin tokens." for $4. Well, maybe this is too strong for $4 - actually I'm guessing it would be QUITE good there, probably printable without the buy even. With the buy, it's bananas in engines, combo decks, and slogs, and not at all bad in big money. I mean, big money likes the smoothing a lot, too, particularly if it's your kind of simple BM, where mostly you are buying silver and gold. 5-cost cards that you want tend to probably push you to not saving so much, and of course most games have those. Anyway, I expect we won't see too many vanilla-like cards with coin tokens - it wouldn't surprise me if Baker is the only one.
Okay, the set-up. Usually, I suspect you'll use this to take a 5-3 opening. Actually I wouldn't be surprised if this makes silver just a lot less prevalent - the main goal of silver, in a lot of decks, is to get you up to 5, which is hard to do without silver in many respects. But here, you've got that $5 locked down. And very often, your $5 will help a good deal in getting to more 5s. 6/2? Well, there aren't all that many 6s I want turn 1. Yeah, goons is pretty good any time, though I think most often this is not so much better than the 5 you were going to get. Altar, yeah. Gold, well, would you not rather have the 5 card most of the time? Particularly when you get to save the token? I think you would. Border village, almost certainly not. I mean, just take the 5, you don't need the village yet anyway. And most of the other 6s, I mean, it's not like I'm oozing for a t1 adventurer or farmland or fairgrounds. 4/4 opening? Well, it's true that 4 is supposed to be there because you can't open double them, but on the other hand, I am not so sure that this is actually true in practice for so many 4s - particularly when you consider that, not only does it have to be 'worth it' in terms of avoiding the terminal collision and what have you, but also in terms of spending the token, AND in forgoing te 5/3 you could have had. So I just don't see this as actually giving much impact at all. And then there's saving it. Probably this is most useful for some boring board where you are playing e.g. Smithy BM. But if you just want a 4/3 anyway, because there are no 5s worth having, or having early, for instance, then you are good there.
The card itself: I imagine it will see some use in engines, just because treasury, market, highway, et al see play sometimes even when they're more or less just peddlers. I mean, I like this better than, say, treasury, but worse for engines than, oh, bazaar and highway, which are both excellent engine cards (assuming you have some buy/gain for highway of course), and even market, which you usually don't want tons of, but then that 1-3 can be really really key. This probably won't be a key card in almost any engine, or deck maybe, but just a nice solid support card... which isn't very good, just because it costs 5, which is a huge opportunity cost! I have to say, I disagree with Stef - this card is TERRIBLE for Big Money - terminal draw. I mean, you are going to draw it dead off of something like smity, it competes with a lot of the $5 draw cards, which will just be better, this leaves... well basically, courtyard. And okay, courtyard won't have this collide (much), but you end up getting fewer courtyards, and given that this doesn't have just oodles of upside for that particular deck... I'm sure it will help that deck some, I grant you, but I doubt it is a lot better. And much of that time even, you'll have something nicer to do with $5. I assume this is best in sort of money decks without terminal draw. Of course, these decks aren't very numerous, because they generally aren't that good, but you see them sometimes. So something like this and monument, this and swindler, maybe even fortune teller and cutpurse and militia, this kind of stuff. Something like mountebank would fit there, too, at least potentially. Such decks currently pick up caravans, labs, stables, this kind of thing, as well as peddler variants, and I assume this will hit in there, and significantly better than at least most of the other peddler-types.
I find it totally unsurprising that BM-this beats BM-Market. Of course, you aren't going to ply either of those decks, really almost ever, without other stuff. If you get the play rules right for this, I bet it's even bigger than that. I mean, market for that deck... you're almost never using the +buy there.