Delve could be said to have several close relatives. Let's take a look at 2 of them.
Masterpiece: The most obvious one. Delve and Masterpiece can both give you a bunch of Silvers instantly with only one buy. The more money you pay, the more Silvers you get. Delve is a better deal up to about $6 or so, depending on whether you'd take free Copper. The biggest difference is that you can buy Delve with a leftover $2 for a small boost; Masterpiece requires a bigger investment.
Scouting Party: Both cost $2, and both give back a buy. But which do you want? In Big Money, the Silver is great at this cost, so you probably want that unless there is only a shuffle or two left. In an engine, get Scouting party if you need reliability, Delve if you need economy/payload.
Other "relatives" are Travelling Fair and Save. I may write a compare/contrast about them and Delve later. Or maybe someone else wants to.
Delve for double Silver in the opening will prove very useful where you want to open a $3 that does not give economy like Ambassador, Lookout, or Smugglers.