We have to go back and see what a pre-amp actually does. In practical use, a preamp is used mainly for attenuation. Even the most basic attenuators have colorations. So I don't see where the claim that there are $1,000 pre-amps that get perfect replicas of the input signal comes from, even at unity gain (which would likely burn something up downstream with a 2v input or higher).
Perfect may be the biggest two syllables in the English language, but you've never seen a $1000 preamp that measures flat enough to be audibly transparent? Really?
We do know that preamps with beefier output stages and power supplies can handle longer cable lengths with less degradation and also have the flexibility to drive different amplifiers with different input sensitivities. So let's look at these expensive preamps innards. Yup, beefy power supplies and output stages usually made up of expensive parts with tighter tolerances.
So beefy power supplies and output stages is one way to add value. Given that the amp and preamp are going to be in the rack together, and if they have flat FR, there is no reason not to buy the manufacturer's preamp that matches your amp of choice, we probably won't have good reason for the beef, therefore the value could be dubious, but it's a value. Are we up to $14K yet?
Tim