Is remastered mainly just less jitter?

I listen to Classical exclusively.  The remastering are almost always superior.  There are none of the loudness issues.  From what I have read the biggest reason for the improvement is that early CD issues of analog recordings featured 14 bit ADCs.  Also several Conductors liked to diddle with the knobs in the control booth and did a lot of damage, so going back to the earlier mixes was restorative in and of  itself