What you have are "states" and all that's being proposed is proportional or party list voting rather than "first past the post" voting ~ for a state.
It depends. Quite often the small states have been noise and the easiest route to a majority was to concentrate on the large states. In recent years smaller states have had an advantage. I would say if PA goes this route it will lose influence. Out of 18 seats maybe 3 or 4 are tossups. However I would say there is a good chance a Republican could win statewide in ‘12 - so it could work against the GOP this time out.