There are 320 instruments in World Suite and 264 in EthnoWorld 6. Many are in one and not the other and if you have both, you are still missing a hundred or more other world virtual instruments currently available, in other collections and solo libraries.
Now, for example, if you decide you want a great Guzheng, you can get one from Best Service/Yellow River, Impact Soundworks, Evolution World, Soniccouture, Wavesfactory, and Sound Magic, and there are probably more I don’t know about. Bolder Sounds has the Vietnamese Dan Tranh, which is similar. Everybody here would have an opinion about which one you should get and I doubt anybody has them all.
Even if you limited your search to a small list of the most important world instruments, what would it cost to go first class with every single one of them? The Sonica Koto alone lists for $240.
This is why I suggested that it’s a good plan to start with EthnoWorld 6 and figure out what instruments you like and suit your music the best. What you like is something nobody can answer for you. IMHO knowing what is a great oud or duduk isn’t relevant to you until you know that you want an oud or a duduk.
Let me say this. I have spent dozens of hours playing different examples of the expensive, well-reviewed solo libraries and I think I know them well. I have also spent a lot of time playing their counterparts in EthnoWorld and World Suite, because it was only through playing them that I decided to upgrade. The world collection instruments usually have numerous articulations and countless ways to refine their sounds. I absolutely disagree with any blanket statement that there are no quality instruments to be found in these libraries. There is definitely a variability in quality, as they come from different sources, and some were sampled a long time ago, but all are good enough to introduce you to the joys of world music and set you on the path to buying other libraries, if you desire. Or, in my opinion--to use. Which I often do.
What is far more important IMHO is how you play these instruments. If you gave a world class piano virtuoso almost any decent piano virtual instrument, it would sound infinitely better than me playing a “better” one. World instruments are exactly like that--people spend lifetimes mastering them. And learning about the cultures and playing styles will help you understand why another library might help you achieve more musical and/or authentic results.
The other big question is: are you trying to make music the way it is done in its native land, or are you just looking for new kinds of sounds?