An exchange membership is an appreciating asset. For some traders, it is the best trade they'll ever make in their life. It is also a lifeline that after you blow out your account, you can sell the exchange membership to buy gas for your cab.
Exchange membership is truly a function of your volume while trading products covered by the type of membership you buy. In other words, if you are doing 5 turns per day on average, then it might not make sense to buy a seat or lease one. However, anyone doing 1000+ turns per month will be complacent if he does not consider buying or leasing the appropriate membership. In most cases, exchange and clearing fees will drop to around 20 cents per turn + whatever commission you have to pay your broker. That is a far cry from the $4.50 per turn most retailers require. It is just simple economics. The appreciating value of the seat, in my opinion, should not be much of a consideration in this decision. The seat will usually fully pay for itself after a short time.