When you're in Cancun use the bus! At 6 pesos, it's one of the few bargains to be found. One evening we spent $7 to visit the Hyatt Caribe by taxi. Silly me! I didn't realize it was only 5 properties away. We walked back for free. Speaking of the Hyatt Caribe, they have a wonderful jazz combo there (been there 4 years, so they'll probably be there for your visit).
I really enjoyed the food at the Beach Palace, probably because I ordered shrimp dishes (oh my gosh, they had 5 inch prawns w/cocktail sauce at one buffet). For lunch, I suggest grilled fish w/tortillas on the side (all you have to do is ask) w/pico de gallo and guacamole. Yum! yum! Conversely, my husband who ordered steaks or hamburgers was disappointed with the quality of the all inclusive food. If you visit Aventura Palace ask for grilled scallops and Ahi tuna. They cook it to order, although there is no indication it's available at the buffet. Also, if you like wine, be sure to try the Mexican wine served at the Palace restaurants. I was amazed at how good it was.
Regarding side trips: DO NOT GO SNORKELING AT ISLA MUJERES. The Isla Mujeres trip was fun, but the number of fish is NOTHING like Hawaii and the crew way over-manages the snokerlers. DO SPEND A SPA DAY AT AVENTURA PALACE. If you ask, the guy in the Beach Palace lobby will take $15 off the price of a service. So for $83 I was transported the 1 1/2 hrs, got an excellent hour massage, was tended by three handmaidens, ate a great lunch overlooking the ocean. Ahhhhh.....
If you're in to saving money, there is a 2 for one dine out card you can buy online. If you want lobster (or a REALLY good steak) one night, it's well worth it. This trip was business for my husband. He attended the Cancun Spanish Language Institute to improve his business Spanish. He highly recommends this school and its teachers. It only costs $200 for a week of intensive Spanish immersion. Finally, if you enjoy great service you'll love the Beach Palace.