+1 Doug Schroeder.
Bottom line is if you are happy with you system, just enjoy the music and stop worrying about upgrading.
Yes, you past the point of diminishing returns as soon as you go past your first boombox.I disagree! Once one experience what's available, they will upgrade or change. Sometimes it's good NOT to know what's available.
The laws of diminishing returns hit early and hard, just as in any other hobby. A $10,000 watch is not 1000 times better than a $10 watch. Same goes for audio gear.Nobody buy $10,000 watches to keep time but an accessory or enjoys collecting them. Same with cars ... The equivalent in audio is always on a journey and never reaching a destination ... enjoy cycling through gear.
Bottom line is if you are happy with you system, just enjoy the music and stop worrying about upgrading.