Though I've never done an extended tour, it's something I'd like to do. As to your question about having money your old age, my justification is that you're going to stop working at some point and have to live off the money you've saved up. Why not "retire" for one year when you're younger, whether you're 25, 35, 45, or whatever? You'll probably get as much, if not more, enjoyment from that one year sabbatical than when you "really" retire.

You'll miss out on some income and even if you work an extra year you'll lose on the time-value of money. But life is about more than having money in your old age. "You can't take it with you", they say.