It's a card many players overbuy. Non-terminal $2 is really enticing, sure, but I've seen way too many "Festival Idiots" who buy scads of them and then use them to buy single Provinces and think they're great, not realizing that they're just playing BM and overpaying for silver. +1 buy is often helpful. +3-4 buys rarely is.
For engine building, it requires GOOD draw cards (+3 or better) and ideally sifters to help prevent stalls, and a greater dedication to trashing, but in the bargain it mitigates it's own drawback: Since it provides money with the actions, you don't have to buy as much economy in the form of treasure and other money payload cards, meaning you CAN do much more trashing and make it work just fine as long as you make your deck really thin.
I'm not sure I would ever use Pathfinding or Training on Festival. That's what cantrips are for. Turning a bunch of $2 Pearl Divers into $5 Labs with upside is fantastic. Turning a $5 Festival into a slightly more reliable $4 Conspirator seems iffy.