Looking at Plaza as an engine enabler
For reference:
Plaza
Types: Action
Cost: $4
+1 Card. +2 Actions. You may discard a Treasure card. If you do, take a Coin token.
As soon as I saw Plaza I thought, that would go great in a Watchtower/Library discard-draw up to X deck, but it would certainly play differently than Hamlet or Festival, the traditional enablers of that sort of deck. It's probably going to work most like Fishing Village in that sort of deck where you need a source of +Buy. Also when it discards it is discarding at least a marginally useful card (probably a Copper) where Hamlets/Cellars/Warehouses will usually start by discarding your worst cards, your Curses/Victory cards. Probably at best a weak draw-up-to-X engine enabler.