Naturally...being Cruise Critic...you will get mostly "unhelpful" answers to your question. Sorry about that.
The actual answer is...yes, you can receive the pin, and no reason not to wear it if you want to. If you don't get it...simply go to see the Loyalty Ambassador on board and ask for one. They keep plastic baggies on hand of the pins.
Though as "Doghog" pointed out...you will not be officially D+ until your points are awarded until after the cruise is complete (5-8 days later) of which you turn the new level. But that does make the next cruise that much sweeter!
Enjoy, and congrats on turning D+! 🙂