Develop is a great card, both misused and underrated. It's a mediocre to poor trasher in the early game, not all that useful when there are better trashers, like remake or chapel. I won't talk much about it's trashing abilities except to say that if there's any better trasher don't buy it. But, it has two great abilities. One: it topdecks. Two: It gives you two cards for one. While getting a silver or fishing village topdecked may be no big deal, in games with a nice mix of 4-2 6-4 or 7-5 cards (which are most of them) it very often pays to invest in one early, with an eye on the midgame. In other games, it pays to buy one later on. Although it's not very good in straight big money boards, the things you should be looking at when you see develop are: actions vs. terminals i.e. can I afford another action in my deck? The lower end cards: like, if I develop a silver will I be stuck with an estate I'll need to get rid of? Deck size. Do I need/want more cards in my deck? Can I afford to topdeck whatever combo it is? And what combos are there? I'll list just a few of the possibilities. Develop a gold to kc-any 5 card. (ghost ship, governor, torturer etc.) develop a 5 card to grand market conspirator. develop a silver to baron estate, potion-secret chamber/embargo/ lighthouse in scrying pool or university games or crossroads silk road. develop a province to platinum bank/forge/kc.
If there are good possibilities, and your deck can afford the topdecking, which is not always the case (sure it's nice to develop something to duchy but if you get it on top next turn you probably won't have enough for the last prov) then the early trashing is an added bonus.
It's a shame councilroom is down, I had a lot of nice develop games there, but if you search my name and develop you can find some here too.