I am using Valladolid as a base to explore ruins in the Yucatan. I didn't want to use Cancun or Playa del Carmen for 2 reasons - one is that Valladolid is closer, and the other is spring break is happening in Cancun right now.
Chichen Itza is an amazing place. There are many tips (with cost) for skipping the lines, but when I was there, the lines was 20 minutes long. And it was shorter when I was leaving. Not so bad as to justify paying a guide 1000 pesos (about $55).
However, the guides can be very useful if you would like to learn more about Chichen Itza. The information throughout is very sparse.
Bring sunscreen! But, if you forget, there are about 100 vendors there willing to sell you a hat.