I have one because I prefer looking AT it over looking FOR it. That said, it depends on what kind of trouble you plan on getting yourself into. They're an extremely versatile tool, very dangerous if you don't know how to use them, but indespensible in certain instances. I bought mine because they're relatively cheap, and if I need it just once it will likely justify the cost. I don't pack it around all the time like a poser - I just toss it on when I head out to the bush.
Buy yourself one, but put it a bit lower on the list. Make sure you have a good axe, a shovel, and a small folding saw before you buy the jack. Read all the instructions and practice using it BEFORE you need it in an emergency situation - using a hi lift is a good way to knock out some teeth if you're careless.