The short answer is “yes”. I know it costs 150 donuts, but there are lots of reasons why the Wishing Well and the Leprechaun are a good use of your donuts. Here are some of them:

1. It’s a limited-time item character and item set – and that means that when the St. Patrick’s Day celebration is over, you’ll probably never have the opportunity to buy either the Wishing Well or the Leprechaun again.
2. Although the Leprechaun doesn’t say anything particularly intelligible, he is a character with a voice.
3. While the Wishing Well doesn’t earn you a regular income, the Leprechaun does. Every time you tap on him, you earn $5 or 2XP (and the higher your bonus multiplier, the more you get). The way it works is this – you tap, he giggles or curses and runs away, and after a few seconds, you can tap him again. You can do this as often as you like! And occasionally, he gives you $20 or 20XP or more, but that seems entirely random and perhaps you’ll need a bit of Irish luck to get that extra bit of Leprechaun gold.
4. The Wishing Well does, however, give you a 4% cash and XP bonus on your cash collections and character jobs.
5. The Leprechaun completes the Irishmen character set, which means you get the set completion cash and XP bonus.
6. All your friends will be a nice shade of St. Patrick’s day green with envy.

And here are some reasons why you may decide to save your donuts for something else:

1. The Wishing Well is kind of small, as you can see here:

2. The Well itself doesn’t earn you a regular income (although, the Leprechaun really takes care of that).
3. For such a small item, it’s really very expensive.
4. The Leprechaun doesn’t have any quests or tasks.
5. You can’t trust Leprechauns.

The fact that it’s a limited time item was enough for me to buy it, though. And the Leprechaun is good for hours of mindless fun!