What are the frequencies I find so refreshing in this?

I don't agree with the harmonic exciter concept.  Because everything would be bright if the whole mix was run through such a device.  Personally I don't like them and they can be a bit of a cop out over a whole mix. They also destroy other aspects of a mix and can make it less robust.
 
I think this track is a good example of what I have mentioned in these threads before about top end.  Only have a few things that are crisp and many other things are way less toppy.  To me the top end is looking up at a dark sky at night and there are not may stars up there and only 2 or three are bright and the others are dull.
 
The hats in this track are crisp yes but if you listen carefully you will hear most other things are not over bright at all. Even the 2-4 clap sound has lots of upper mids yes but then it sounds like it is rolled off at the very top end.
 
Yes some of the ambient synth sounds are crisp but not overly and then other synth sounds are very warm. Also notice how all the top end stuff stops as well and the track goes very ambient and warm with no highs at all.  So your ears have time to recover in these parts.  Then the hats come back in nice again.  Kick sound is not over bright either.  Vocals are very smooth as well.
 
It is just well balanced top end wise over all the tracks.
 
Many get this part wrong.  As your ears get tired after you have been mixing too long you tend to over brighten things a little and also you tend to brighten everything which is also bad.  If everything is bright then nothing is bright!  When everything is bright your ears start shutting down to cope and then everything ends up dull! (So then you start to brighten things more so you are on a merry go round now!)
 
You only need one or two things in a whole track to actually extend up into the crisp area of 10K and above. Try it and you will see. Many things are not normally that bright in real life.  Use that information.  When you keep the bandwidth limited on multiple tracks things become easier to hear and start to sound more separated.  Putting highs onto everything damages this to some extent.
 
The HP filter is your friend down low to keep the low end under control but also the LP filter is your friend up in the high end to manage the top end of your tracks.  When you do manage your high end nice then what starts to happen is your ears actually open up a bit while mixing and the top end becomes clearer!! When you feel this is happening then you are on the money top end wise.