What do I mean by a "story?" It's a sequence of consecutive strips that tell a story that builds between them. They may stand alone, but you get something extra out of the strips if you've remembered the prior strips in the sequence. This is what separates stories from the sequences we've had before, which were not sequential and thus Schulz could not expect a reader to remember prior strips in order to get a joke in the current one. There might be continuity, such as with Schroeder's musical talents, Charlie Brown's checkers losing streak, Violet's mud pies or Patty's ability at marbles, but Schulz sets each strip up as if the prior strips didn't exist. These strips work alone too actually, but there is obviously a thread that connects them, they are meant to be read together.
We had one prior sequence that could count as a story, the "Lucy in the Golf Tournament" Sunday strips, which are atypical Peanuts strips in many ways. To my memory, this is the first story-related sequence to stretch over four consecutive non-Sunday strips. (One could consider all Sunday strips to be in their own sequence, since Schulz probably drew them on a different schedule and some newspapers only carried Peanuts on weekdays or Sundays.)
This is the first time we've seen a drawing of Pig-Pen clean, which is a different enough design to almost count as a separate character. He looks like a cross between Shermy and Linus, in overalls.)
Violet is talking about career; one could interpret Charlie Brown as talking about something more profound.
This is the first strip in the story I mentioned above. We had Pig-Pen drawn clean on Monday. Now we can imagine Schulz amusing himself by drawing some of the other characters dirty in Pig-Pen's usual style. Pig-Pen's messiness extends virally to several other characters. First, Schroeder.
The question of people admiring Pig-Pen is interesting. I think there is something admirable about him, but it's not specifically his messiness.
Next, Snoopy. Although a dog is kind of expected to be dirtier than people, here they seem to consider him of the same status as the other kids.
Charlie Brown speaks in bold, but he doesn't look angry. It looks to me more like he's dismayed that he's gotten messy like the other kids, only to find out it might not hold the advantages he was expecting. (Whatever those might possibly be.)
If the kids allow themselves to be "influenced" by Pig-Pen so easily, I can only say that they're unusually vulnerable to peer pressure.
The pay-off strip. This isn't the first strip in which we've seen Patty dirty -- there was an earlier one in which she and Violet were making mud pies. I don't know what it is, but I always thought Patty looked quite charming messed up like this.