My experience is at the Disney World stands--Main Street, Disney Springs, and France Pavilion.
No, the frames aren't worth it. The silhouettes fit a standard 5x7 frame and you'll find a better and cheaper selection at home. Plus they add unnecessary weight to your luggage or even just carrying through the park. The portraits themselves are 2 pieces of cardstock that must be carried flat. I've never had one damaged placed carefully in a backpack or suitcase.
We never waited through more than 3 other parties in line. The attendant can tell you the best time to return if the line is too long. We sometimes sat on the curb with a snack to pass the time.
The artists are various personalities. Some are very chatty; others are silent. They all appreciated being asked to sign and date their work.