I would say "no". Of course, it all depends on how much money you have and how you value it...

If $300 is about what you'd spend on a nice dinner, then you might as well buy the membership. Of course, if you're spending that much on dinner, you're in for a rude awakening when you enter any of the clubs...

As FrequentHopper pointed out, were you to make it to Gold (or above), and were you flying internationally (and Mexico, Canada, and the Caribbean don't count), you'd have complimentary access.

Bottom line: It doesn't sound like you travel frequently enough to maximize the value. But if you've got the extra money, it does provide a nice and quiet respite within the normally-chaotic airport environment.

Sean