I fly about 10 to 15 times a year on the same airline. Should I join my airline's airport lounge?

Will,

The quick answer is yes. The cost range of membership in an airline lounge is from $100 to $300. Depending on your history with the airline, you may even obtain membership for less. Let's consider the economics of this investment. If you paid $300 for your membership and flew 15 round-trips a year, your average cost would be $20 per trip. Your actual per visit cost is less since you would be flying 30 one-way flights, most likely with interim layovers. This could bring your cost down to $5 per visit. This is a small price to pay for the comfort of waiting-out a 2-hour delay in a luxurious room that offers refreshments and comfortable seats.

Joel