Festival seems overloved IMHO; i find its really a 4.5 worth card. At 4, it would still be worse than chapel, and where it sits at 5, Festival usually winds up looking like a bad afterthought (esp when sitting with a couple other 5s). Its main use is as a final engine part, mostly in engines that could find a way to win with other cards on the board. City costs 5, Minion costs 5, Torturer, Margrave, Council Room, etc. City is even a Village-type card 
Festival isn't really a replacement for any of those other cards except City, and unless those Cities activate, Festival is clearly the superior card. Sure you're not underestimating the power of the +$2? That's really where the power is: not only does it provide two important engine components -- extra Actions and an extra Buy -- but it gives you a huge chunk of the payload as well. So not only doesn't the rest of your engine have to work as hard to get to Province/Colony level, but if it
does overshoot, you've got the extra Buy to make use of the excess.
Festival is also a particular enabler for Library/Watchtower engines (where the disappearing coins are key) and Minion engines (where non-terminal coins are key, +Buy might be important, and +Actions let you slip in other terminals).
Finally, Festival is a rare engine component that slips into money decks okay too, because it's essentially a Silver-with-a-bonus. It's probably unusual to want it in this capacity, because, since money decks don't overshoot your target amount as much as engines do, Festival's +Buy is probably less useful in a money deck. But it's useful in a money deck more often than most Village-type cards.
