So to sum up, the issue we're debating is whether Death Cart is viable as a long-term trash-for-benefit, or if it's best used as a one-shot. Personally I lean toward the former, but everyone seems to be disagreeing with me.
The bigger problem is that you aren't listening to nor talking about why people say it is a one-shot and why you think it should be good for long-term TfB.
Space efficiency, odds of pairing Dthcrt with its fodder, needing an action, tempo concerns, sustainability, etc. these are issues that you blithely ignore for reasons I don't understand. I've done a worked example showing exactly how one-shotting a dead Dthcrt & replacing it with gold/silver gives you 5 provinces for only one more card of draw.
You aren't doing a good job until you address these concerns legitimately. Maybe I'm wrong about Dthcrt becoming a weakish gimped gold when you can't feed it Ruins, fine, tell me why. Why do you think Dthcrt/Money is actually viable on a lot of boards? Why do think it is better than Dthcrt/Engine? Why don't you want to sift for Ruins?
I could have sworn I at least started out saying that Death Cart doesn't do well as a Big Money thing. I'm sorry for blithely ignoring.
Death Cart/Money - this is probably not a good strategy - a sustained Death Cart needs Actions, and with Big Money, you're not going to be colliding Death Cart with anything. One-shotting the Death Cart can slingshot you to Golds or Platinums, but then you're left with Ruins in your deck.
Death Cart/Sifter - yes, you can use this to find your Ruins to trash, and then you can use Death Cart as just a three-shot (or four-shot with Shelters). But if you have Death Cart, Warehouse and three Coppers, you may as well just eat the Warehouse and get a Province.
Death Cart/Engine - this is probably the best. You're buying lots of Actions anyway, you usually have +Buy to make full use of the $5, and you're usually drawing your entire deck, so you don't have to worry about collision.
I guess I didn't articulate properly with the cheap Actions thing. How about this: only do that if you have +Buy, or are in an engine. What I'm trying to say is that you get the most out of Death Cart if you can keep it going.
Maybe I should compare this to Moneylender. Moneylender is awesome - it gets rid of your Coppers, and it gives you coin. When you're out of Coppers, Moneylender is now a Confusion in your deck. Do you buy more Coppers to feed to Moneylender? Most likely not, barring Goons or something like that. Perhaps it is best to think of Death Cart as a Moneylender analogue - you use it to eat up those Ruins (and maybe your Necropolis), and as an added bonus, it takes itself out of your deck when you're done with it.
But the fact that it gives $5 should give you pause. Moneylender has 7 targets, unless you're being Mountebanked. Death Cart only starts off with 2. So while you don't normally have to worry about Moneylender running out, you do with Death Cart, because it will usually run out of Ruins before the game ends. So while you wouldn't normally spend a +Buy on Coppers (again, except maybe for Goons) to keep feeding the Moneylender, it might be worth your while to spend a +Buy on a $2 non-terminal. You spent $4 on Death Cart in the first place to get $5 out of it - are you saying that you now won't spend another $2 to get another $5? And again - this would be if you had +Buy, and typically in the context of an engine.
I seriously need to overhaul this article.
Am I making sense? Or am I still blithely ignoring something?
EDIT: I've also noticed that with Death Cart and Procession, you often find yourself blithely (heh) chewing up Actions you normally wouldn't, just because they happened to collide. One game, I fed a Merchant Ship to a Death Cart to win. One of my recorded games has me Processing anything and everything, even with no $6 Action on the board, and it was the most fun I've had with Dominion in a while. It gives games a delightful sort of "ah, fuck it, let's do it" attitude.