The Debut Carbon is so good at $399 there's really nothing to discuss until you get to the RP3. I took some of my LPs to a hi-fi shop to audition an amplifier and I was *shocked* at how good the Carbon is. It's my unequivocal recommendation at $500-600 and under. The smartest $100 you can spend is to get a Debut Carbon over a Debut III.
Maybe not, if you get a good enough turntable. Check the sales figures; LP sales have handily eclipsed SACD as the high-res medium of choice.
Just a way for me to enjoy some certain recordings on occasion that I enjoy more on vinyl than on digital. 90% of my listening will remain on CD/SACD.