"...what I can expect by upgrading [my CD player]?"
Like all audio upgrades, you can expect to feel happy with the improvement, or to feel you have spent too much, or to vacillate between the two perpetually. Most dangerously, you can feel your audio appetite only stimulated by the upgrade, not at all sated. You may find yourself wanting more, and more, andÂ… well, it can get silly pretty quickly.
Seriously, as a general rule, I have found that if done wisely, upgrading your source will always make you happy if you love music. There is no substitute for getting more musical information in the audio chain, which is what a good source does. And of course, what constitutes upgrading wisely is auditioning as much equipment as possible before you buy.