What Sonically is the Difference between a $1,500 CD Player and a $10K-$25K One?

All CD players regardless of price are subject to the deleterious effects of vibration and background stray laser light. Therefore, one would be better off buying an inexpensive player and fixing those problems than simply investing beaucoup bucks on a player. There are obviously many other related issues such as interconnects, power cord, fuse, external DAC, etc.

No matter how much you have in the end you would have had even more if you had started off with more in the beginning. - old audiophile axiom

I recall a comparative test years ago between a Sony Discman and a Theta transport/DAC. A Boulder preamp/power amp were used with Quad 63's. The result: NO Difference! The French chef applauds! 

The difference between an expensive and cheap anything in audio is the exceptional room, set up and gear you need to hear the difference. Without all that the money is mostly wasted.

+1 jafant and wlutke .  Significant difference in sound quality, but without comparable gear and great room certainly not worth it...

In terms of measurable distortion? Nothing.

And its been that way for decades. After some 30 years of using various CD players my two personal favourites were also the least expensive. Not necessarily because of their sound more likely because of my low expectations. I really wanted my far more expensive UK race tuned Sony models to sound better, but they didn't. Even the filters made bugger all real difference.

What you might get instead for paying more are features such as Bluetooth, switchable filters, looks and build quality.

Album art display is pretty cool too.