From what I have observed of P he had made efforts over the years to establish himself as a 'person of substance' but nothing has ever really stuck, and often things get thrown back in his face. There is only so much backfire one person can take before asking "is it really worth it?" On the whole I get the impression that he is done with the whole 'eternal crown prince' gig and would probably like to just get on with life but can't while C is still alive. Things might change after C passes away (not for a long time - touch wood) as Nikolaos is more popular with those who care about these things.
Honestly, to me (I'm in a charitable mood at the moment) P seems like he is bored, restless, and can't find his place in the grand scheme of things (mid life crisis?). Think about it this way - his cousin Felipe is now king, as is Philipe of Belgium and WAX of NL; and Frederik, Victoria, Haakon, and even Prince Charles will be too in time as well. P probably could live with this when they were all princes, but now more of them are ascending the thrones of their respective countries, or coming close to, that's a hard pill to swallow on a gut emotional level, even if you can reconcile your self to it intellectually. Compare to MC, who for all her egregious character flaws seems happy with her buisness, tacky lifestyle and motherhood - probably because she never had anyone have expectations of her as a child and young woman, she doesn't have the dilemma P is facing. All things considered, given the fact that P won't ever be king isn't his fault, its not impossible to imagine that this might be a source of friction between him and C, who does bear some responsibility for the position P finds himself in? Having the sins of the father visited upon the son, so to speak, is never easy to live with, and neither for that matter is the lingering question of 'what if' in the back of your mind either.
Undertaking the kind of work mentioned above is hard slog and not for everyone. Especially if it wasn't something you asked to do in the first place. Being heir to a deposed house inst the same as being heir to a reigning monarchy; you pretty much have a lifetime of being stuck in a social/political twilight zone and the fact that if you try and be politically involved you look like a quixotic ninny, and if you try and do somthing independent you're accused of being an upper class twit. In other words dammed if you and dammed if you don't. I do agree that the jet set lifestyle, or more accurately the open flaunting of said lifestyle, is bad taste and speaks to a certain lack of self awareness on their part, however things could be a lot worse - look at the ex royal family of Italy!
Sorry for being long and slightly off topic. This was just an attempt to look at the issues from their point of view and provide another angle to help the debate along.