JP's got it right, Abysmal gas mileage (Why I don't own one) very prone to rust (All 80s AMCs were) also they are full of electronics (Power everything), and none of them are new anymore. Gremlins are common. Parts can be tricky, but there is a large following of Wagoneer enthusiasts, and anything can be had.
They drive very nice, and have all the gadgets. very posh, and very retro. Always a classic look with a vintage canoe on the roof racks.
Oh, and make sure you budget for a new wardrobe of flannel shirts from Woolrich and LL Bean.... ;D