Although I still say go for it, I would actually also advise taking a class or at least visiting a shop and trying it out. It is still more physical than some people think.
You can also take in consideration the amount of tops you have, the rate at which you piece, and if you don't buy the machine are you willing to send them out for quilting? You can have a lot of quilts finished very nicely for the price of a long arm.
My last thought was to compare this purchase to a car. If you are still driving, if your car died tomorrow would you replace it or would you say you were too old?