Yes, I also thought that Dark Ages's "upgrading cards" would be more like what you describe, eHalcyon, although I pictured an upgrading city rather than a bonfire. I'm glad the Travellers are more varied than that, though (Spoiler: Warrior is not [+$1; Gain a Treasure] and Treasure Hunter is not [Gain a Treasure]).
My use of Twigs and Bonfires back then was just a joke (derived from the Dark Ages flavour text), and the simple, consistent effects were just for clarity. I was only trying to describe the chaining, not come up with an interesting line.
Just to comment on the other two previewed cards --
Lost City looks really strong. If somebody had posted this as a fan card, I would probably have commented that the drawback did not seem to be enough. I am either overestimating the vanilla bonuses or underestimating the drawback, probably a little of both.
Early on, a single Magpie is a lot like a Peddler in that you expect it to draw you a bonus Copper (for $1). The bonus is increased cycling from actually drawing another card. Having a larger hand is often good too (though sometimes bad). It can be better than Peddler when it draws a better treasure than Copper (later in the game) but it can also whiff when it flips a non-treasure. Gaining another Magpie may be good or bad depending on whether you want more Magpies, but they are cantrips and they don't force you to trash cards, so they're not nearly as bad as Rats. They get in the way of terminal draw and they make Magpies less useful overall (more actions getting in the way of treasure-finding).
I am now caught up in the conversation, hooray! I am surprised there aren't more pages of discussion yet, but I guess it is still early.
PPE: Is this "Bacon Cheeseburger" talk about the prototype card names?