From that area, going South is boring.
Going north from Port Clinton is definitely the way to go. You get to the Pinnacle and Pulpit Rocks, two of the best views in PA (or the AT?). Yes, the Pinnacle is crowded on weekends.
It is a great area, but you need to be wary of the camping regs. Rangers have been very strict about camping in the area only at the shelters, and have been ticketing those they find in other places (near the Pinnacle, e.g.). So, if you go stealth, make sure it is really stealth, and not lazy-stealth.
You can do a long day (15 mi) and go from Port Clinton to Eckville shelter, going thru the Pinnacle, and many other woods. One the way back, you can bypass the Pinnacle and use some other trails to get back to Port Clinton in about 8 miles.
Another option would be to park at the Hamburg Reservoir lot (must register for overnight parking - 610-562-7821), and hike up to the Pinnacle, and back down, and use some other trails in the area, and stay at the Windsor Furnace Shelter (~1.5 mi from the HR lot).
Map info here.
Spring between Pt. Clinton and Hamburg Reservoir
Water source at Windsor Furnace shelter near Hamburg Reservoir
Water source at Eckville Shelter
All other water sources in the area are typical of the PA AT; down 1,000' (vertically) off the trail/ridge. This is not fun to get to, so plan wisely.
The Pinnacle really is a great area. I do a handful of hikes every year with my friend up to the Pinnacle to see the full moon rise over the valley, then hike down the fire road under headlamp. Really amazing.