.. i purchased the D7500 after selling my D7100 and to me there just wasn't much difference between the two ..
I have not owned either one, but this is what I have learned:
After reading about both, and watching several videos, one can conclude that the D7500 is misnamed, as it should have been called the "D5700", as in; the next step in the D5xxx line. When Nikon named it the D7500, people naturally assumed it would compare with the D7xxx line, but it simply doesn't fit in that group as well as in the D5xxx line. This is probably why you didn't see much of an improvement going from one the best APS-C cameras in the Nikon brand; the D7100.
The D500 is an epic win for enthusiasts of the Nikon brand cameras. You should notice a huge improvement in the auto focus and the dynamic range, as the D500 is phenomenal in low light. It is reported to be able to focus and make a photo in conditions that are so dimly lit as to be difficult for the human eye to even see the subject.
The D500 is very well suited to sports/action/wildlife, if that means anything to you. Have fun with it!