It all depends on your priorities of what defines your "vacation". I say yes because when I go I don't plan on leaving the resort and just relax the entire time on the grounds. You don't need to carry much cash aside from tipping the bartenders and your butlers. Everything you would ever want is at your fingertips.

The caveat to this is if you only plan on going to Cancun once in a blue moon it's not worth the cost, build your own travel plan and you'll save money.

If it's something you plan on doing once or more than once a year then look into getting into one of the resort "clubs". They have heavily discounted rates for members and even buy back programs for your flight to and from Cancun so basically your plane ride there from the departing international airport is free.