Okay, I'm back.
So, dondon, you made a whole bunch of claims in your last post. On the face of things they all seem perfectly plausible. Why is it, then, that they don't jive with my experience? I'll try to reconcile them.
When you are building your deck, getting rid of an Estate and replacing it with a good card is a much more substantial improvement than simply adding 2 good cards to your deck.
That seems plausible. However, when the proposition is specifically either getting rid of an Estate and gaining a $3 card or gaining a $3 card and a $5 card, it starts to look a little hazier to me. Granted, you have to trash a $4 card to do it. But once you get to the actual scenario of either trashing an Estate for a $3 on your deck or trashing a $4 card to get both a $3 and a $5 card on your deck, I'm firmly in the latter camp at least 50% of the time, and that's a conservative estimate.
In your specific Caravan example, the Caravan itself is a desirable card to have in your deck because it improves engine consistency (if you're not building an engine, Develop is pretty bad).
Is it?
Fascinating.
So you want to keep that Caravan in your deck. Unless you somehow still have an Estate in your deck near the endgame, the best move is almost always to play the Caravan, hope you draw a Copper (if there are decent $3s on the board like Village, Menagerie, Oasis, etc.), Develop Estate -> Silver or other $3, and buy a $3.
I'd say that which is the better choice is a lot more nuanced than you're making it out to be. It can depend on what's on the board, what's likely to be at the top of your deck, and many other factors. Let's move down to the next example, where you're just plain wrong.
EDIT: A simpler scenario is, what would you do with this hand: [Develop, Caravan, Silver, Copper, Copper]. Too many players would just play the Caravan and trash a Copper if they didn't draw a better target. I'm fairly certain that's nearly always the wrong play.
Play Caravan. If you draw a Silver or some other non-terminal way that can get you to $5 even with Develop on Copper, then Develop Copper. If you draw a Copper and need a $5, then don't play Develop at all.
Let's run through this twice, using both scenarios you present. I'll use the term Power5 to designate some decently strong $5 card (Wharf, Mountebank, whatever).
Option 1: There's a Copper on top of your deck.
You play your Caravan, drawing the Copper. You don't play your Develop. You play your Silver and 3 Coppers and buy Power5.
I play Develop, trashing Caravan and gaining Silver and Power5, putting them both on my deck. I play Silver and 2 Coppers, buying a Caravan.
Let's take stock of our deck status. Neither of us lost a Caravan, and we both gained a Power5. The only difference is that I have an extra Silver (or other nice $3 card).
Now let's look at our next hands.
Your hand is six random cards from your deck: [?, ?, ?, ?, ?, ?]
My hand is [Power5, Silver, Copper, ? ?]
Man, looks like I edged you out there, too, and probably by a significant margin. Huh. Well, let's take a look at the other scenario. Maybe you make out better there.
Option 2: There's a Silver on top of your deck.
You play your Caravan, drawing the Silver. You play your Develop and trash a Copper. You play 2 Silvers and a Copper and buy Power5.
I play Develop, trashing Caravan and gaining Silver and Power5, putting them both on my deck. I play Silver and 2 Coppers, buying a Caravan.
Our decks look a little different here. I still have a Silver on you, buy you've trashed a Copper this time. I'll be generous and say that's a wash.
Here are our next hands:
Your hand is six random cards from your deck: [?, ?, ?, ?, ?, ?]
My hand is [Power5, Silver, Silver, ?, ?]
Wow, my hand is even better than before! Nice.
Here's the fallacy with Develop: if you trash a good card, then you don't get to play it. That hurts your current turn. You maybe could have just bought the card that you would have gained anyway if you played your good card and used Develop on something else. You don't gain the card at -$1 if you eschew Develop on the good card, but in general, removing a bad card yields a greater improvement than adding a good card (and if you can do both, that's really good!). You don't get to topdeck a pair of cards, but consider that unless you already have a combo going in your deck anyway, what's topdecking a pair of cards going to do for you? Say you topdeck a Village and a Torturer but you have no other Torturers in your deck. That's not very useful. Say you topdeck a Market and a Silver, then draw $7 next turn when you really just wanted $5.
That all sounds really plausible, but have you actually tried it? You claim that it's more powerful to remove the Estate from your deck ASAP than it is to topdeck two good cards, but what evidence do you have that that's actually true? I'm not asking you for a proof or anything, but maybe you should try it my way before you convince yourself that you're right.
Furthermore, the topdecking slows down the rate at which you cycle through your deck, so while you get to see your topdecked cards immediately, the other cards that you gained during the shuffle appear later.
Well, that's just misleading. Those cards you're topdecking should be at least as good as the cards you're buying. Also, once you've reached the endgame, you should be topdecking good Actions and Treasures and buying Victory cards, making the negative cycling incredibly valuable.
What I mean is that Develop has its niche where its cuteness can be powerful. But you have to draw parallels to it and other TfBs: for example, cards like Salvager, Remodel, Apprentice, etc. that do like to trash expensive things. Most of the time, the reason you get them early on is to get rid of those Estates, and maybe clear out a couple of Coppers when you have the chance. Then as the mid- and end-game roll around, you can take advantage or their more powerful abilities.
So what you're telling me is that because other trash for benefit cards prioritize trashing Estates over good cards in the early game, Develop must work the same way. Why? That's a big logical leap.
EDIT: Sorry if my tone isn't cordial, but after your quip about my Effect With, I can't say I feel too badly.