I've got completely restored C-1 about a fortnight ago and I've been playing around with her since.
I always reckoned that the best preamp is no preamp, but the C-1 convinced me I was wrong. Before the C-1 I was using Sony TA-E88. I was using it mainly because of the MC head amp and an input for my reel to reel deck. TA-E88 is a good preamp, she does what she's supposed do, adds volume control and some additional inputs and doesn't cock up the sound in any way but she didn't add anything either. However, when I replaced the Sony with the C-1, I've noticed two major differences. Better instrument separation and better detail reproduction. I had my mate come over to assess the sound, if it's not just my imagination or wishful thinking. He heard exactly the same thing as I did, and he also fancied a deeper bass (which I didn't notice). Nevertheless, the difference wasn't that big to justify steep prices of hi-end pre-amps.