Hi Robert, and welcome to the world of scuba.
I firmly believe that nitrox is the one speciality that is beneficial for every diver. My wife completed Nitrox (Enriched Air Speciality) when she had 12 dives, so you don't need to wait for more experience. . . just do it.
Nitrox is just a term used to describe a breathing mix with Nitrogen and Oxygen. Technically air is Nitrox with 21% oxygen. Usually recreational nitrox refers to breathing gasses with more than 21% oxygen and less than 40% oxygen. Practically 32% seems to have become common and is often offered in places like Bonaire.
In terms of the benefits;
1. You will find that the no deco limits are extended. This allows for more bottom time, either as a single long dive, or spread over a number of dives over a day or week. This is the primary benefit that divers would think about - more diving.
2. Some claim that they feel more invigorated after diving on nitrox. There is a mixed view on this and there is no scientific support that I am aware of. My personal point of view (based on me only) is that this probably does apply to newer divers that might not be diaphragm breathing and hence are taking shallower breaths.
3. Some claim that diving Nitrox is safer. Again the view is mixed. If you dive Nitrox based on air tables then yes, there is an additional safety factor. This is however, quite small as the air tables themselves are already conservative. The debate is whether this marginal "safety benefit" is offset by the negatives that I set out below. Also, if you dive to the no deco limit of Nitrox, then there is no additional safety when compared to diving air to the no deco limit.
So basically, only benefit number 1 is undisputed.
In terms of drawbacks;
1. You need to know what is in your tank. Therefore before each dive you spend about 20 seconds analyzing and marking the tank contents onto the tank.
2. Nitrox (and air) have a maximum safe depth that they can be used at for recreational purposes. You need to make sure not to exceed your tank's maximum depth. This is the key risk as prolonged exposure to higher partial pressures of oxygen can cause Central Nervous System (CNS) toxicity and lead to underwater convulsions. There is, however, a lot of safety built into the Nitrox usage as you will learn it and therefore if you follow the rules, you will be fine.
3. Prolonged exposure to higher concentrations of oxygen can cause your lungs to become rough. This will repair itself once you stop diving. It is highly unlikely that you will be able to do enough recreational dives to have a problem. I was diving 5 or 6 dives of 45 to 60 mins a day for a week in Bonaire and didn't come close to an issue.
4. Nitrox fills can be more expensive.
So as I said at the outset, to my mind the knowledge and ability to use Nitrox are worth the course.
Galapagos in 3 weeks. . . cool. I have not been there myself, but have heard that the diving can be difficult with currents and surge. Be careful and try stick close to the guide.
Bonaire . . . more cool. I have dived there and benefitted tremendously from being able to do 5 dives a day on Nitrox. Conditions were easy and well suited to a new diver. The shop I used gave a fee upgrade to Nitrox, so it was a no brainer.