The Inflatable Gorilla and Baboons comes from the same episode as Frink’s Robot Dog: season 24 , episode 9, “Homer Goes To Prep School“. It appears in a dream sequence as Homer has an out-of-body experience following an injury during a fathers’ fight at a children’s fun center. The Gorilla and Baboons are how Homer sees a Santa and Reindeers Christmas decoration while he’s unconscious, as you can see in this video:

Is it worth 30 donuts? Surprisingly, it is, especially when compared to other similarly priced decorations. It offers a 0.75% bonus on all cash and XP collected from jobs and rent – the same as the slightly more expensive Frinkosonic MHV and the Giant Grasshopper. This is also the same amount as the non-limited time Piece-of-crap Car, and slightly more than the Ambulance, which both also cost 30 donuts. However, unlike all the others (with the exception of the Giant Grasshopper), it’s animated and sways gently in the breeze that apparently blows over the device you’re playing the game on.

As with many of the other Yard Sale items, it’s not an essential purchase, and it’s probably more a matter of how you see it fitting in to your Springfield. Also, as it’s from a dream sequence, it’s not a “real” item, so you may also choose to bypass it for that reason (but then you’d also have to by-pass just about every Halloween building or decoration for the same reason!).

To help you out, here’s a screenshot of the Inflatable Gorilla and Baboons outside my Duff Stadium, where I’ve also put the Duff-Barney Blimp: