Nice NYT article (click here) on the introduction of yoga in America, that brings up great questions of what the cultural and economic climate have to be like in order for yoga to catch on at all, and then how those things determine what yoga looks like. And the perpetual question, what is authentic yoga? It's not like yoga is an antique vase and we can call in "Antiques Roadshow" to tell us, no, that's fake, or yes! that's real!!!! Priceless!
Whatever our motivations may be, I think it really can't hurt to just do it. The benefits, on all levels, come to us whether we know what we're getting into or not. Yoga always benefits me in ways I never expected. Sometimes I don't even notice for years. Even if you don't KNOW you're doing it for spiritual transcendence (and i'm not entirely sure on the meaning of that myself), you'll still feel better, act nicer, and love more.