Well the Prince in indeed at the wrong place the wrong time! Things were pretty tense in those chapters. I think that the two chapters reveal more information about Gania's character (to tell the truth I didn't like him from the beginning). He is an ambitious man, he likes money, he will do anything to be part of the high social class and he is embarrassed about his family. It is really funny how mad he gets when Nastasia pays a visit and in the other hand it is funny the whole scene with the Prince opening the door. My favorite part is the dialogue of the Prince and Nastasia(quote taken from the same link mentioned in the article):

---"Your portrait struck me very forcibly this morning; then I was talking about you to the Epanchins; and then, in the train, before I reached Petersburg, Parfen Rogojin told me a good deal about you; and at the very moment that I opened the door to you I happened to be thinking of you, when—there you stood before me!"
“And how did you recognize me?”
“From the portrait!”
“What else?”
“I seemed to imagine you exactly as you are—I seemed to have seen you somewhere.”
“Where—where?”
“I seem to have seen your eyes somewhere; but it cannot be! I have not seen you—I never was here before. I may have dreamed of you, I don’t know.”
The prince said all this with manifest effort—in broken sentences, and with many drawings of breath. He was evidently much agitated. Nastasia Philipovna looked at him inquisitively, but did not laugh. ---