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

Elizabeth said: "Well MY digital is great, and so is my analog."
Voice of reason.
Some of my digital -- even redbook, is glorious. Much of it is terrible. Some of my albums are glorious, some are terrible. HUGE POINT HERE - often its the SAME recording that is glorious in both formats. Case in point: "Ella and Louis", Verve recorded with two mics onto a Studer A-77 in like 1961. Recordings matter. Mixing matters. remixing and digital masterings matter. Format, to me, is less important if all the above are done correctly. Sadly, they are not, and early digital recording, mastering and pre-eq was just terrible. No mystery why those sounded as they did.

KEY POINT #2: both formats are capable of excellent sound. Perfect? Of course not. Neither are LPs.
Now, back to the OP’s question - which was basically around the incremental value from $1500 to $15,000. This is a subjective matter, and a slippery slope. Just as racers inevitably wind up with dedicated race cars, trailer, trucks, etc., so many audiophiles wind up with crazy-costly systems. I only hope they are well chosen and enjoyed. but its likely not necessary - I’ve heard very good sound from iTunes, Bitperfect and a Schiit BiFrost Multi-bit.
Above i noted where some differences can certainly exist. I’m currently evaluating how to hit the 80/20 rule on many of them. My personal opinion is that the biggest differences today, especially for the dollar spent, come from speakers and sources, both analog and digital. You can get really, really good electronics for more modest spend (note: i design and [hope to again] sell electronics, I’m stabbing myself in the back).  Note that "modest" might range form $1000 - $6 or 7k, and some speakers are very challenging loads, while others can be driven by an NAD 3020 (like Vandy 2s).   While cables no doubt impact sound i find the benefit/$$ ratio wildly bad - better spend that money on speakers or DACS (or a great TT/arm/cart). Oh, that’s still a tough area of electronics - RIAA stages for low output cartridges...

I went to a demo by the guy from stereo magazine in the padoo room and he did proper back to back comparisons of the same recording cd v vinyl. Vinyl sounded better to my ears. He explained that when a stylus moves in a groove it is like the thickening of a line on a seismograph- it is actually a distortion that we like.

10,000 dollars .

itsjustme I agree.  What bothers me is that my London/Decca opera LPs sound so much cleaner/less distorted than the comparable CDs, most of them digitized in the 1990s (just compare the choral parts of Turandot/Mehta-the CD is distorted).  I don't have that problem with any other classical label (7,000 CDs in my collection).  I have many wonderful 1980s jazz CDs from Contemporary and Japanese CDs.  I also have terrible/awful remasterings of mono RCA opera from the last few years (the 1980s transfers sound 90% as good as the original LPs, the new ones have cut off bass and highs, forward bright sounding mids, compression-yuk!).  Many Amazon reviewers seconded that conclusion.   Luckily, I have many Kevin Gray remasterings of all genres in both LP and CD formats.  

For my listening pleasure, I spent a ton of money on my listening room/acoustics.  Next is the cost of my analog front end.  Digital front ends can sound great even if they aren't expensive nowadays, unlike the 50-75 CD players from the 80s and 90s that I tried.  Speakers are very important in the chain and lucked out using great older speakers rather than new ones at a pittance of new price.  I get SOTA cabling from a manufacturer as a beta tester and the rest of the electronics are custom made at a low price as well (my second CD only system costs $5k yet sounds better than 90%+ of audio show gear-simple but perfectly matched tube gear and 25 year old speakers).  

Matching good sounding components is the key to good sound after accounting for the big elephant in the room-the room itself.  I use Hallographs and SR HFTs to tune the room perfectly.  Those are items generally not found in audio shows or audio salons.  Too bad as their cost relative to their merits is well worth it.  One can use lesser equipment in a great room but ruin great equipment in a poor sounding room.

My two bits.

It is all about pounding your chest when you have your buddies over to show them your new stuff.  It is then very important to tell them what you spent so they can all be extremely impressed.  Then ask one of your buddies to do a blind testing between the old and new CD player to see how much difference you can hear for the $20,000 difference.

Reminds me of the story, "THE EMPEROR'S NEW CLOTHS"!  

Then you buddies turn to you as ask, "HOW MUCH DID YOU PAY FOR THAT THING"?  Kind of reminds me of the Smuckers commercial.  If it's Smuckers it has to be good.