There is definitely a lot of backwoods/unexplored rock in PA. I love route exploration and the FEELING of climbing a new piece of rock. I say FEELING, because so many times have I been on a hunk of stone, pulling off vines and loose holds, only to find an old soft iron piton 70 feet up the route. To be honest, I don't really care if I'm the first or not. What I like is that feeling of the unknown. Not knowing how hard or how protectable a piece of rock will be, and trying to unlock its puzzle.
One of my mentors claimed to have climbed in over 400 areas in PA ALONE! That was hard for me to believe, until he would take me to all of these backwoods crags, and I would realize that within 5 miles there were 10 more just like it!
My advice to you would be to do as much research as you can. Use USGS maps, google earth, aerial photography, topo maps, and see how they coincide with the rock that we have in PA. I'd say that one of your most valuable resources would be the Pennsylvania Climbing guidebook, and his website paclimbing.com. He lists a lot of backwoods crags that are seldom visited, and hints at others in the vicinity. This will get you acquainted to where our rock resources are, and will give you a good starting point for where to hike deeper into the woods.
PA might lack the MASSIVE crags that other states provide, but we do have a lot of variety, quality, and quantity of small (are some big) crags. As for PA's variety, I think we have climbing on nearly every major type of stone. Sandstone, quartzite, schist, conglomerate, gneiss, shale, granite, schist, argillite, slate, diabase, bassalt, limestone, etc....
I have found crags that have absolute GEMS on them. Routes that would be classics anywhere. Some of these crags only have 5-10 routes, but how many routes do you climb in a day?
So go out and get exploring!