Vietnamese is the official language of Vietnam, originally created by the first Chinese settlers who influenced it and are responsible for certain words and tones.
If your curiosity for Vietnam is limited to the time of a trip, learning Vietnamese may not be necessary, but knowing a few words is certainly an asset, and certainly an opportunity to exchange a few smiles. Just as in our own country we appreciate when a foreigner speaks to us in our language because we don't understand his or her own or because we appreciate his or her effort, Vietnamese people will be surprised and delighted when you do the same.
As you have understood, with 6 different tones and 6 possible meanings, if you don't have a musical ear it will not be easy to learn Vietnamese. But as a counterbalance, grammar and conjugation are relatively simple.