[MrDibble]

Vanilla didn't really replace anything. The kind of thing where it's used, like custards and baked goods, used to be spiced with a variety of flavours but no one dominant one. So cookies might be lightly spiced with cinnamon and ginger, a custard may be flavoured with elderflower, or a creme would just be eggs and sugar and cream. If anything, possibly "treacly" would be what it replaced, since a lot of sugar would have been less refined.

3 old world plant foods the OP missed:
common (Phaseolus) beans (which largely replaced broad beans in a lot of cuisines)
Peanuts, which have largely replaced other ground nuts
Squashes and pumpkins (Cucurbita pepo) mostly replaced other gourds

Oh, and turkeys largely replaced Guinea fowl.

Originally Posted by Broomstick

I think turnips served in the "potato" role pre-Columbian exchange. Probably other root vegetables like rutabagas/swedes, too.

Parsnips were quite common. 8