My Spanish isn't nearly as impressive as some around here, but I for one am very glad I speak it.
As a blind monger, I cannot count on facial expressions and hand gestures, so speaking the language is key for me, but for you... don't sweat it.
Learn the following:
Numbers, basic Spanish pronunciation, gracias and con mucho gusto (thanks and you're welcome), and perhaps the names of various body parts.

Yes, you'll have much more fun with each advancement in your Spanish proficiency, but if you're just going to do business at Zona Blue, Hotel del Rey/Key Largo and/or Sportsmen's, you won't need much.
One of the pivotal moments in my Spanish-speaking life was when I made a joke and one of the chicas actually gave up a belly laugh. She wasn't laughing at my Spanish (I hope), rather she was laughing at the punchline. It was fun. Also, having Spanish can help quickly resolve problems that may arise.
My strongest advice is this: Do as others have suggested, make a little effort. In addition, find a gringo or bilingual tico wing man who will accompany you and interpret for you. It was my very great pleasure to help out several CRT bros on my last trip by translating for them, and I'm sure other proficient Spanish speakers wouldn'[t mind, either.