Super tweeters, are they worthwile?

Instead of invest in superteeter invest in a good dac will improve your dynamic , soundstage and seprarste , do a research about a dac and get the one work for your system 

I have used Heil AMTs as super tweeters with good results on several sets of speakers over the years.  With some speakers they don’t seem to make an improvement.   But I built my own crossover and you are looking for something turnkey. I hope you can find ones that you can try without having to keep if they don’t sound they way that you want. Good luck. 

I use the Sopranino’s with TAD’s. The integration is seamless. Imaging and soundstaging are unchanged, but this could vary with placement of the tweets in relation to the mains. The main benefit is the more ‘alive-sounding’ quality that they impart. It’s subtle, which is how they are voiced.  The effect is consistent for all types of music. I can’t imagine how they wouldn’t benefit any dynamic driver setup.

Please take a look at the white paper and all the material that's available to you for Townsend Super Tweeters. I bought These and used them with my old B&W speakers with excellent results. Those speakers reached up to 20K hertz.
When you get it right the results are similar to that of using a subwoofer i.e. when you integrate a subwoofer correctly your high end is also improved. Similarly when you integrate a super tweeter correctly the low end is also improved.
Keeping the discussion around the frequencies that we actually hear, we all know that most of us can not hear past 16-17K hertz. However; a lot of instruments produce frequencies way higher that 20K hertz. the effect that these devices have is by reproducing those higher frequencies they introduce a tidying up and organizing effect to the entire frequency range  which obviously includes the frequency band that we can hear.
So the effects of super tweeters are more profound when you play analogue sources as they do allow much higher frequencies than 20K hertz.
Going back to my own experiences when I upgraded my speakers to ones that would go upto 40K hertz, I packed the Townsend Super Tweeters away, thinking that they were redundant now.
After a few years the curiosity got the better of me and wanted to try them out with the new speakers. The Townsends go up to 90K hertz !!
And low and behold the positive effects were also noticeable then (may be not as profoundly as the old speakers).
Now the beauty of Townsends is that you can completely switch them off by a dial at the back (as well as having multiple gain setting positions).
So with the help of one other person you don't even need to leave your listening seat to make before and after comparison or between settings.

Also please research the number of high end speakers that actually include a super tweeter. There has to be a reason for that !!  

Op, you're correct in wondering if a cd quality recording has any information at that high a frequency.  It doesn't. Perhaps a wider dispersion tweeter would be more beneficial for you? I like the idea of upgrading your dac as well.