You're a man after my own heart, especially when the Interstates are also toll roads. I do this whenever i can. My first step is usually to assume that I'm driving in the early 50's when the Interstates and even most state turnpikes didn't exist. The US highway system was the driving backbone then and it's still there. For me, the main route that I'd be looking at is US-15 with alternatives US-322 and US-522, switching to state highways in New York.

Depending where exactly you're starting from in the DC area, you'll need to find a 'local' route out of town to the northwest to avoid I-95 and Baltimore. You'll also have to decide if you'd rather drive mostly in the mountains (US-522/322), along the Susquehanna river (US-15), or some combination thereof. Another option would be to swing wide around Baltimore and head for PA-611 up through the Delaware Water Gap. And, of course, as you noted, you can take one route up and a different one back.

With the time available to you, you'll have plenty of time for silly scenic funky sites. Two good places to start a search to see what interests you would be HERE and HERE.

I would think that this is going to be an iterative process where you tell us if anything we tell us piques your interest or not and we respond. I hope I've given enough to get you started.

AZBuck