I strongly believe that Aman's can only truely be enjoyed when money is no object. I have often been disapointed as my expectations are always too high.
Any Aman in Asia is the best bet for a truely outstanding experience. But if money is any problem, you will not enjoy pre dinner drinks, and be chocking on your main cours, not to mention your sleepless last night as you convert the pre check out bill into $ or équivalent.
My first Aman was Amankila in Bali, toulk a helicopter flight arround the island, did the works and had a faboulous time. But for that kind of money you can do the most amazing things in life, so it's up to you realy, but if it is just to spend one night to be able to add it to your list, it is not worth it.
You can add an extra month to your RTW trip per night you would have spent in an Aman if not more, so depends what objectives you have set for your trip and the budget you have.
Have a great time