If you learn MSA and speak it fluently, Arabs would actually respect you (although a lot of them would find it quite amusing, as you would be speaking in a “Shakespearean” form of Arabic.). You will have no trouble with regards to getting your point across in MSA, since it’s the lingua franca of the Arab world, BUT you will find that sometimes, when an Arab is speaking to you, you won’t have a clue what he’s on about (especially when talking to Moroccans). That’s because Arabs don’t speak MSA in their daily lives, they tend to only use it for reading and writing. As for speaking it, well, if the person is in a formal environment, he will use MSA (news broadcasts, religious sermons etc).
I know this because I only know how to communicate in MSA, not in any of the dialects (although, to be fair, some of the “dialects” are so incomprehensible that in my humble opinion, they shouldn’t even be considered as part of the Arabic language). Learn MSA. Trust me, you won’t regret it.