High end stereo preamps? Worth it?

In a blind test no preamp can improve upon no preamp.

That one needs to be etched in stone, as another great audio saying.
Just like "it all starts at the source, get that right and your almost there" (Ivor Tiefenbrun Linn Sondek)

Cheers George

Give Prima Luna  a look.  It was a noticeable immediately.  So much so, I thought there may have been something wrong in the preamp it was replacing...Wasn’t the case, It just sounded wonderful...

I noticed a difference going from a NAD preamp to a Don Sachs. A little in the dynamics and a little in the delicacy. Put it together and tou get a little better sound.

And I can vouch for Primaluna. Running the Don Sachs into a Primaluna Evo400 power amp is a great combo. 

Totally worth it if you have other good things in the chain.

I just added an Airtight ATC-5 between my DAC and my amp. An obvious difference, more musical, dynamic and relaxing.