Value of a preamp?

I agree with most above. And yes, there are very good solid state preamps.

A good tubed preamp will greatly enhance your sound period.

There are always lots of a variables, but that was certainly the case when I upgraded. I’m sure technology has progressed since then, but the move from a Hafler DH100 to a Lazarus Cascade Basic tube pre was pretty significant. It brought the system to the next level, and gave me the ability to roll tubes to tweak it. It drives my Dyna/VTA amps extremely well, which is one of the critical parts of that elusive synergy. It became a pretty incredible foundation to build a system around. There is no single right answer, but even a modest tube pre sure worked out well for me.

It can offer so many benefits if you have the right one. Soundstage, clarity, dynamic contrast, slam & dynamics, imaging, details, separation of instruments & vocals, etc. 

Can greatly enhance the overall sonic characteristics of a system. Tonality, dynamics, soundstage, and so much more, when it is the right fit with everything else.

It can't add anything but can color the sound in a manner that some find positive.  

Jerry