The only artifact I can reliably hear in 320 kbps MP3s is pre-echo, for instance with castanets, and only in a few very specific situations. Apart from this, V2 and above sounds completely indistinguishable from the original to me.
but what if in the future you could hear the differences? And now your entire collection is in MP3 V2 - now what?
No reason to not rip everything in uncompressed FLAC these days.
But if your happy with your audio now, great!
And even though you may have diminished hearing you still have awareness of frequencies above 8Khz.
Imagined artifacts will probably remain or might even increase though, since people typically have much higher spending power at 40. :)
I worked in audiology for my entire 30's and tested my own hearing (biocalibration) once a week.
Never once saw a reduction in my hearing thresholds (250Hz - 8kHz)
Nor have I read any supporting documentation that agrees with a reduction of 8kHz thresholds before the age of 55.
https://www.sciencedirect.com/science/article/pii/S089662731...
Stick to FLAC and keep your fingers crossed for cochlear regeneration tech ;)