High end stereo preamps? Worth it?

First- one premise made by the OP is incorrect- phono stages are not noise free. Some are very quiet but none are dead silent. 
Next, I’ve been messing around in this audio world since the 1970’s. Everything makes a difference and a great preamp can make a system and a dud of a preamp can break a system. More so, I believe, than can different amps. 

IMHO.... It has probably made the most significant change in systems I have owned in the past 35 years.
1980 Something... DQ-20 speakers, Adcom GFA 555, Amp GFA 565 preamp SOTA sapphire TT  ..
I went from the Adcom GFA 565 to a CJ Premiere 2.
I was completely blown away didn’t need to do an A.B. test...That was the catalyst that put me on the quest for Audio Nirvana.
YES !!!!! 

I think you need a decent preamp in any system.  I used to have an Audio Research Hybrid Preamp in the early nineties and for my DAC I have the Wadia Digital.  I loved my Audio Research until it broke after three years of use.  While looking for a replacement or trying to have my preamp repaired locally, I used my Wadia Digital which has a volume controller  temporarily thru my Krell  amp.  The sound was not as warm  with the DAC preamp as my Hybrid Audio Research  so I ended up going for the newer products. Now  my Preamp is solid state now which is a NuForce and I also switched my DAC to the Benchmark unit .  My Wadia is still in use in my bedroom system .  So the answer is a good preamp is vital to a good system and better as a stand alone than a preamp with DAC.

imThorek

So we know the higher end preamps don’t include dacs and phono stages. Highly desirable noise free devices. I hear wonderful things about these preamps, Luxman, Accuphase, Audio Research, etc.

Are they as good as represented?

there is no one size fits all answer to these two questions. the first question is whether a high end preamp is worth it.

up to a certain investment point in a total system, a preamp holds you back. this is because a stand alone active preamp adds a layer of interconnects and power cords and noise. at lower levels of quality those artifacts are bigger than the dynamic additions the stand alone preamp adds. you are better off using an analog preamp in a dac and eliminating a preamp and tasking that budget elsewhere. the tipping point for this question is not definable; it will depend on the level of gear you are using, if you are using multiple sources, and whether your dac preamp can handle the source switching.

past a certain point of system investment and performance the stand alone preamp takes you further. but it will need quality ancillaries to be at it’s best.

at the highest system performance levels stand-alone active preamps are not only worth it; with very rare and expensive exceptions they are essential.

the other variable is the quality of the preamp in a dac you might choose. for instance; i own the MSB Select II dac; which has a passive preamp inside it that will surpass many/most active stand alone preamps. and also it’s capable of accepting a source input so can be used with a phono stage. it it a remarkably capable preamp; but......the MSB Select II is hideously expensive. it takes my also quite expensive darTZeel 18NS preamp to surpass the MSB Select II passive, and then only by a small margin. if i was digital ’only’ i would not be using my dart preamp.

the second question you ask (not directly) is whether a high end preamp can have phono stages included. my dart pre has very fine phono stages (2 of them), yet performs at a high level. it is the resident preamp in Michael Fremer’s system too. and there are other fine high end preamps with internal phono stages. so ultimate preamp performance is not exclusive to those without phono stages.

I agree with most of the other, a preamp can make a huge difference. I went from a Rogue Cronus integrated with a nice tube sound to Belles amp and Audio Illusions preamp. the amp provided all the umph and power I was missing but the preamp (tubed) brought that tube sweetness and sound stage that I love. So, yes I believe they do make a difference. SS or tube and cost will be your initial marks. read and get knowledgeable. listening is imp if possible. I bought mine blind but from credible source that also own speakers like mine. Be aware that some preamps have extra features like MM/MC. that could be handy down the line. Happy hunting!