Went last year for my honeymoon. Enjoy your time and the excellent service. Shows every night on one side of the resort, found those to be entertaining. We chose to visit Tulum due to it being a lot closer, the trip you have was all day affair vs a 3-4hr excursion. Load up ya resort points on spa treatments for both of ya, never thought I would care for this but i found it to be enjoyable.
We took the dolpin swim excursion across the street, solid treatment there, delivered as promised and just haggle with the staff some, you can buy your pics and cd for a good bit less than the initial asking price.
Shopping and people watching/drinking were good in playa del carmen. Just stay in the organized areas, plus we never ventured at night due to the night life at the resort, always a show or other couples drinking etc.
My advice is eat and drink well, enjoy the moment. Staff is top notch and I was pretty happy with our choice to go there, would definitely go back.
Cliff Notes: drink, relax, frick, drink, dolphins, frick, eat...rinse and repeat as necessary.....just dont drink so much ya try to frick a dolphin!
Enjoy yourselves and Congrats man!