The fee-waived checked bags and priority boarding are two sides of the same coin as I see it.
1. bags are free, if you choose to check them, that is a big plus for every single flight.
2. Because bags cost more, more people are bringing them on board and taking up that overhead space. Being allowed to board early means you definitely get a space above your seat if you yourself decide to carry on.
--
Those two, in addition to priority seating, are huge. Those who disparage these benefits would do well to book a y ticket on any airline that is not in *A and see how much fun it is.
I fly US Airways semi-frequently and definitely feel the positive effects from being a *G on that carrier as opposed to nothing at all.