Using my own 38 year experience, I think you will still enjoy it, maybe even more when you see how much there is to do offsite and how much money you will likely save even with the car rental. You could even take a road trip with your own vehicle. It is a bit of a ride from Philly but if you take routes that bypass DC it is not that bad. I'd probably aim for staying overnight along I-95 somewhere near the bottom of SC or the northern part of Georgia and then a more relaxing drive to the WDW area. Not everyone likes road trips so I understand that. Personally I love them and for 28 of my 38 years of trips to WDW it was from Vermont.
Driving is cheaper then flying plus staying offsite, heck you might even come home with more money then you left home with. That, of course was a joke, no one ever goes to Disney and comes home feeling financially solvent.
I cannot speak for anyone else, but just thinking about the money I'm saving makes me smile more than any fake opulence that Disney can paste together. And there is so much to see unshackled from the World of Disney to the real world. I go for the parks, nothing else appeals to me. I hate paying 5 star prices for 3 star meals and although most of the resorts (moderate and High End) are nice, I only spend my sleeping time in the rooms. I don't need shiny stuff when my eyes are closed.
I drive in now from Raleigh, NC. Door to door it is almost exactly 600 miles and 10 hours driving time. I leave home a 6am and usually arrive around 4 or 4:30pm. People fear the traffic and I will say that it is crazy sometimes but, remaining alert and aware makes it not much different than Philly, I would suspect. I have never had a problem and I have never been there without my own car or a rental. To me it is not a big deal and remember I am from Vermont originally where a traffic jam is when you are the third car back from the intersection waiting for the light to change.
Granted it is easier now that I have been that many times, but the roads are well marked and Waze is your friend.