Maybe it’s always been this way, but it seems the latest trends in indie bands are to either go really big or pare everything down. Examples: The two-person, girl-boy pop duo has exploded, not to mention the two person blues combo. Power trios seem on the rise — run-of-the-mill rhythm guitarists need not apply. On the other side of the spectrum, The Arcade Fire gains a member every time they tour, collectives like Broken Social…