Is it worth upgrading a CD player?

Absolutely! Check out the Project DS 2, a player with a coax output, meaning it can be used as a transport, too

Many + reviews. Here's one:

I forgot to mention my cd collection is ripped to an external drive and then either streamed through the house via Sonos or played directly to the DAC via a USB cable from a Mac. I still manage the music library using iTunes.

I went from a Marantz CD5004 to a McIntosh SACD 85 paired to a McIntosh MA352. While the DAC in the McIntosh is an improvement, added SACD capability is the most significant. I will note the little old Marantz still sounds very good in the same set up, but there’s richer details with the McIntosh; enough to justify the significant expense differential? That’s up to the individual.

Also noted, there’s limited availability of SACDs and not all are exceptional, when you have a great one you’ll know, it just stands out. Maybe that’s the reveal, you can tell the difference between really detailed and flat CDs and SACDs.

Another mod was I also added balanced cables from the SACD to the MA352 (never compared them to RCA, but couldn’t resist using that option). So many options for SACD players today, but not so much material in that format, you’ll have to hunt for it online.

Another point, I use a Marantz NA6005 for streaming, but I optically connect it to the McIntosh MCD85 to use the newer McIntosh DAC for conversion to analog.