Twitter Land - STEAKA : https://www.youtube.com/watch?v=e_qQEU_uGjw
Chimera - DECO*27 : https://www.youtube.com/watch?v=c6HKcNVbByc
Start Up! - Nariyama Ryo : https://www.youtube.com/watch?v=LFOV9NbkiJM
My name is - yanagamiyuki : https://www.youtube.com/watch?v=1hj3BDehQGc
Dance with me - Osanzi : https://www.youtube.com/watch?v=n37kZTKbpSM
Highlight - KIRA : https://www.youtube.com/watch?v=AYUNaQaDfa8
Ghost city tokyo - ayase : https://www.youtube.com/watch?v=lWl5viCqGSc
Aqua illumination - PedestrianP : https://www.youtube.com/watch?v=F02fIei8gZU
These songs might be pedestrian (heh) to you, but there is so much niche and experimental all using the same voice--I find this highly fascinating.
The above songs I think give a pretty wide longitudinal view of Vocaloid music and the variety you can find in the fandom, from just Hatsune Miku as the vocal.