You don't get extra damage from 2H weapons, aside from the larger die.
Extra damage comes from attacks that do 2x or more weapon damage, which is to say, nearly every encounter and daily power, and every attack at the epic tier. Also as you note, PA gives you much more bang for your buck with using 2H weapons.
The space between base 1H and 2H damage is much less, but then you don't lose much by giving up a shield, either, unless you have a bunch of shield-related powers. Which you probably don't if you're focused on using 2H weapons.
Extra damage comes from attacks that do 2x or more weapon damage, which is to say, nearly every encounter and daily power, and every attack at the epic tier. Also as you note, PA gives you much more bang for your buck with using 2H weapons.
The space between base 1H and 2H damage is much less, but then you don't lose much by giving up a shield, either, unless you have a bunch of shield-related powers. Which you probably don't if you're focused on using 2H weapons.