I think there's huge value to learning Latin, but that's because it was the core language of European civilization for millennia more than because it's a gateway to English.

Ancient Greek is a very difficult language. It takes a solid decade of work to learn, and the payoff is you get to read a few - admittedly brilliant - authors. I would not automatically prefer that to being able to talk to everyone in the Spanish-speaking world - or to learning la belle langue. Also, I don't think Greek was ever learnt by the majority of pupils.