this topic gets brought up a lot. and it can always be confusing for new divers.
it is my opinion that the padi aow course is a waste of time and money. so unless you are determined to only train through padi, and the specialties of interest require you to have the aow cert, then why bother?
i say this as someone who did the padi aow course. but in my case, when i did it, i compared the cost of the number of dives in the course to the cost of buying that number of boat dives and it cost me almost nothing extra. so doing it made sense.
if that is your situation, then go for it. never hurts to get extra training in the water and learn some new theory.
we always hear people concerned about a dive op not allowing them to dive certain sites without padi aow. and this may very well be true in some cases. this may simply be a dive shop policy, or an insurance requirement, or a rip off to try and sell a course.
in my personal experience, i have never been turned away from doing any dives. i found that at most, the shop may want to see you in the water before they decide to take you to certain sites. then they base that decision on your actual skills, not on a cert card.
so my opinion (for what it's worth) is if you believe you will need it to dive somewhere, then do it.
if you need it to continue your dive education with padi, then do it.
but if you are looking for a better option to actually learn more, i would look into the specialties you mentioned and do the full courses.
nav may not be required by any shops, but i think nav was one of the best skills to learn. especially if you ever start diving on your own without a guide.
buoyancy should be a divers number one skill to try and excel at, so if you need help with that, take a good course.
deep is also a good course if you have a good instructor who can help with in water skills and theory. i would hope most shops would accept a deep cert instead of insisting on an aow, but it is up to the shop. i would suggest if they dont, they are just looking to sell the aow course.
nitrox is a course many divers take. there is a lot of good theory to learn and it will be required for many advanced level specialties if you think you may want to go down that road eventually. and yes, it allows you to purchase nitrox. but if you never plan on using it......