I don't consider Bose overrated. When the 901 first appeared I can not recall anyone in the informal audionerd society I was a part of liking it in any way, shape, or form.
With all the positive things I've read on AK regarding vintage Yamaha, Kenwood and Sony, no way these can be considered underrated.
For those into the cache owning the best - Mercedes, McIntosh, and Rolex pop immediately to mind - one cannot overrate them because they are simply the best. That said, I wouldn't trade my IWC for a Rolex except to sell the Rolex, buy another IWC. Then I could buy another tuner with the leftover $$. Not that Rolex doesn't make a nice watch, because they do, it's just that there are better watches out there to be had.
Underrated - Berning, Music Reference, original VTL lineup.