It looks like nobody has a really strong idea, which makes me feel a lot better about posting mine.
The first thing I notice is it surprisingly doesn't seem to play nicely with most other attack abilities in and of themselves. It doesn't stack with most discard attacks, while Cursers and deck inspectors just give them garbage that they're happy to discard, nullifying Urchin almost entirely and Mercenary to some extent. Knights/Swindler/Saboteur likewise raise the proportional number of junk cards, I suppose. Torturer and Mountebank might be interesting exceptions because of the mindgames over whether or not to discard a Curse.
But what the attacks might do is slow the game down enough that you can get Mercenaries and use their trashing effectively. Mercenary trashing has the potential to be blazing fast, combining the raw thinning power of Remake with the deceptively valuable cycling of Masquerade. And although it doesn't toss you Silver or other assorted valuables like Remake, it DOES grant buying power that few other trashers can match. It's very luck-dependent, and maybe it craps out eventually*, but in the beginning I think it ought to be worth something like 3 coins in a deck with heavy Treasure (or with enough +Actions not to draw your Actions dead). I mean we're talking 2 coins plus Cellaring 2 cards, which ought to be worth at least one more coin on average. (Imagine that you're getting +$1 for each of the cards you trashed and it's almost comparable to Vault, if you like.) All that AND trashing AND an attack! The catch is perhaps that you should be ready to trash the occasional mid-value card, especially if you don't have any good way to increase your hand size and find the real garbage. But hey, you wouldn't mind Expanding a Silver to a Gold if it came down to it, would you? So maybe you just chuck that Silver to keep the Mercenaries chugging as long as possible!
So that's my thinking. I almost feel like, why even bother building an early economy, if this is worth so much money? I'd be interested to try wild stuff like going straight for 2 Sea Hags and a pile of Urchins (buying Urchin over Silver), just enough to make my opponent miserable before rapidly grinding down to a thin deck of expensive power cards. (Of course, it depends whether or not an engine of that description is available! Or maybe you can actually load up on Gold this way but I'm not quite THAT optimistic about Mercenary just yet.)
*Does anyone else feel that Dark Ages is really slanted toward decks that wreck themselves at the end? Save up a bunch of Spoils for one big Province rush. Trash all your good cards for their on-trash benefits. Death Cart, Procession, Counterfeit, Beggar. I guess it's the flip side of the "upgrading" theme: this set favors rapid changes in deck composition and the greening phase is certainly an example, but not one that I've seen many people discussing.
