I'd also agree that Develop is underrated, and that it is a better card than Chancellor.
Chancellor does have uses other than linking with Stash, but they're combos for weak boards, generally, or from the fact that its a +$2 action that costs $3 (which can be useful on Vineyards or Scrying Pool boards) rather than because its Chancellor.
Develop, on the other hand, is a card that often lets a more skilled player gain the edge over a weaker one. It turns one card into two, with exactly twice the total value. It changes deck composition, so allows you to transition out of early game cards (like moneylender or baron). It topdecks, so it lets you set up one-off combos of cards you might otherwise struggle to draw together (like turning that IGG into a Gold and a Remodel, or into a Border Village and a Salvager).
It rewards clever brinksmanship, as it works mostly in the low to midrange where stuff like duchy, gardens, estate and tunnel sit.
Certainly Develop is not normally a good opener, and its far from being as all-round zippy as Remake or as versatile as Remodel, but the more I play with this card, the more I see its utility. Its subtle, its clever, its hard to use, but its really not a bad card at all, if you use it at the right time and in the right deck. My favourite Develop play at present, I think, is developing a redundant $4 card into a Develop and a $5 card.
To me, Develop is undervalued if you try to view it as a card you build a strategy around, or a whole deck around. Where it comes into its own is when you view it as a card that can give a slight edge in other deck types, and to make your complex deck that little bit cleverer than your opponent's complex deck.
Chancellor, in contrast, rarely improves a toolbox deck overall, but rather works well in a few very specific circumstances.