re: Is Philadelphia a decent long weekend trip?

If you’re looking for historical sites, maybe try Charleston or Savannah instead?

If you’re set on doing something up northeast, I recommend flying into Hartford or Boston and getting a car to drive through New England.

There’s a lot of literary historical sites: Mark Twain and Harriet Beecher Stowe houses in Hartford. Emily Dickinson and Edith Wharton houses are a short drive across the MA border in western Mass.