I feel your pain. I too don't really hear much past 15K.
That specific tweeter may not be as useful to you as it would be for a younger person, but all of the speakers you mention have their own "sound" that includes the rest of the spectrum. When you listen to these speakers you are either going to have a preference for them over other speakers or not.
Every product you buy, whether audio or otherwise, probably has a feature or two that are somewhat superfluous for your needs. That shouldn't keep you from buying it if the other performance aspects are perfect for your needs.
That specific tweeter may not be as useful to you as it would be for a younger person, but all of the speakers you mention have their own "sound" that includes the rest of the spectrum. When you listen to these speakers you are either going to have a preference for them over other speakers or not.
Every product you buy, whether audio or otherwise, probably has a feature or two that are somewhat superfluous for your needs. That shouldn't keep you from buying it if the other performance aspects are perfect for your needs.