I wouldn't specifically agree or disagree with your assessment, but ....... used bike prices DO vary significantly and for a range of reasons so I think it's difficult to assess when prices 'across the piece' can be defined as rising/stable, etc.
I think it's fair to say that almost ANY specific make/model of bike will command a good price if it's in good nick and got a good history. Heck, you can even see prices of things like, OH, I dunno ..... a Honda CB 200 (not exactly the most exciting, exotic or desirable machine) reach ridiculous levels. And I strongly suspect this could be proven true of almost anything - there will be exceptions, of course (GPz305 anyone?) but as a general rule, if it's good it will be worth good money to somebody that REALLY wants one!
The one thing you say that I would NEVER argue with is that you regret px'ing the 2012 STR!! But a 2010's got the right headlamps (
) so you're not really losing out by getting back in to the older version now!