This IS a very complex and interesting topic. Have a studio that is tuned carefully to flat response and a listening room that is catered towards dense orchestral sources.
Find that the studio is crystal clear but in a direct way that many listeners would find unappealing -- especially over time.
In the listening room have tuned the entire system and room with REW and JRiver so that it is flat from 16 to 30k within +/- 5db. This is my listening preference and can easily hear each orchestral section (or soloist) in the soundstage.
However, if I boost the bass around 5db more I grant you that age and other considerations mentioned above makes the overall sound more exciting. And boosting the treble around 3db increases the presence and makes all sound closer to you (this works if, as Elizabeth noted above, your treble response is without noise and distortion).
Should you be doing correction, keep in mind that impulse response is just as important as frequency EQ in making the soundstage come alive.
An excellent topic for a thread and one that many will have different, but equally good, responses.