I'm having a dilemma about this myself.
Fortunately it's too cold/wet to be an issue at the moment so the decision may be offset until next Spring.
1) My view before 2015 was that getting to the start line of PBP is an incredible achievement in itself.
The effort of doing the qualifiers, the effort of getting to Paris and the impact to your family life warrant wearing the jersey in my opinion.
That implies getting to the start line and crossing it for some distance.
2) That was my view as a successful finisher in 2011.
3) Now I'm a DNF (after 800km) myself I really feel a bit of a fraud but, by my own rules (they are somewhere on the forum I expect) and considering I rode to/from Paris in a 1400km adventure, I'll probably wear it next year.
Remember that many people drive to the event and many have motorhomes waiting at every control.
It's never an easy ride but I can assure you that I would have finished again this time round if I'd had support in a Motorhome at Loudeac.
4) If I hadn't gone to Paris then I'd Ebay my jersey. There is no way I could wear it if I hadn't gone to the start. That's entirely my feeling though.
5) If I'd gone to Paris but was forced into a DNS then I'd be in more of a personal quandary. I think that would tip the scales in favour of Ebay for me. However, it's a souvenir of the ride so maybe I'd keep it and put it on the wall as a memento with my other bits.
PS. The Gilet is another matter, I'm wearing that.
