Is there any one piece of vintage gear you most wished you owned?

I don't know if it meets the criteria for 'vintage', but in '98 or '99 I tried out a Mesa baron that I always kind of wished I would have bought.

I don't think I would have been happy with it for the long haul, but it was fun to play with. 

Also go with a Revox B77 Half Track

I do have two vintage items purchased from my wish list, NOS Revox A77 half track and 80's era Klipschorns.

https://www.itishifi.com/archives//2010/02/klangfilm-euronor-theatre-horn-system.html

the Klipshorn to own from the past would be one of the first twelve ever built.  They had Western Electric 713A compression drivers in them.  These days, you can spend north of $20,000 per pair just for these drivers, and that price would be worth it given what those drivers deliver soundwise.