Over the years I've owned 11 different CD players and 8 different D/A converters. Each has represented the latest pinnacle of technology for that time. When the 24 bit chipsets became available, they were the single largest improvement in my front end. Even my first generation 24 bit dac sounded much more like an ultra high end turntable, or reel to reel master recording (which are my references as what a makes a great digital playback front end).
I realize that the "extra" 4 bits should be technical overkill since the recording only starts with 16 bits. But how else can I explain the sonic improvement with 24 bit upgrade? I have a couple dacs that have identical power supplies, output stages and clocks and the 24 bit versions are much more analog sounding. I should also note that my last two 20 bit D/A converters were no slouches either! They both contained Burr Brown's absolute best 20 bit "K select" dacs! Yet my next D/A, with only cheap Crystal Delta Sigma 24 bit dacs, was MUCH better sounding in terms of depth, soundstage size and preservation of space!
Personally, I'm glad that many manufacturers chose to go with the " 24 bit overkill" chipsets. Until 24 bit chipsets became available, I never could get into music with the same lust and passion as with my analog rig!
Note: It is important to realize that it takes MUCH more than just a 24 bit converter chipset to make a killer sounding CD player or stand alone D/A converter. Many CD player and D/A manufacturers blow their latest 24 bit designs by using poor sounding output devices, cheap clocks and/or crappy power supplies. These unfortunate design decisions make their "latest generation" CD Player/DAC's sound worse than a very well designed older generation 16, 18 or 20 bit digital front end. That being said, I still FIRMLY believe that 24 bit chipset(s) are ABSOLUTELY needed to produce the "best of the best" from digital playback. If you want to get the closest to the master tape with your digital set-up, it MUST contain a 24 bit chipset IMHO. Think of the 24 bit chip as a 12 cylinder engine. You can make a powerful V-8 but starting with a 12 cylinder engine always gives you more to work with (even if it seems like overkill). 24 bit chipsets are NOT marketing gimmicks when done right! They're the real deal!!