eat at Chefs in Buffalo, get the spaghetti Parm, thank me later.

Do Niagara falls. US side is fine, but you need to go EARLY if you want to park anywhere close to the falls. Canada side is cool - kind of a mini las vegas kitsch.

Then head out towards Rochester. Find a place that has a garbage plate. Get it with a hot dog/sausage. Bring some tums.

Do the church sites, palmyra is cool. make sure you do the Whitmer farm, its well worth it, in my opinion.

from the church sites, you can take the i-90 to albany and then down to NYC or take the smaller highway down through binghamton. Also, Boston is "only" another 6 hours from Rochester - worth checking out if you want to really make it a whirlwind.

you could also drive to albany and ditch the car, and take amtrak to NYC. You dont need a car in NYC - its more of a hassle than anything and you're looking at at least $50 a day to park. 3-4 days in NYC. Plan on doing two things per day - one thing before lunch, one after and you guys wont go insane from all the walking.

Then you can take the train to Philly. You only need a day in Philly proper - depends on how many cheesesteaks you want to sample. Liberty bell and independence hall are right next to each other.
In Philly, rent the car and head out to gettysburg. that will take a day. Drive to DC, stop in Harpers Ferry on the way to DC.

DC has decent public transportation and parking isnt great there either, so ditch the car once you get to DC.
Eat at Bens Chili Bowl - despite it being tarnished by it being Bill Cosby's favorite restaurant, its real good.
Ive done DC on the Fourth, and it surprisingly wasnt insane.