The Wishing Well costs 150 Donuts to stick in the ground, but in exchange you'll gain access to the Leprechaun character.
There are no jobs associated with this character, but you can tap on him in exchange for 2 XP. After 10 taps, you'll receive 25 XP.
The Shamrock Topiary is awarded to players when they have completed the ninth section of the St. Patrick's Day event involving Homer, Willy and Tom. This is a very expensive vanity item, so make sure you have plenty of spare cash before shelling out for it!