Elfred's Alley is certainly worth having a peek at with its all too well preserved row of typical homes from the 1700's, but there are lots of great old buildings scattered around the city with less picture snapping tourists standing in your way.
Unique Suggestions: If going to Elfred's Alley, go mid-week, early morning to avoid the crowds. It is a charming place when they are not around.
Fun Alternatives: Look for other great old homes and buildings in Philly. It's full of them.