Preface: I actually have no opinion, have never really bothered to directly compare a specific CD recording to SACD (multi or 2-channel) in any sort of critical (even sighted) listening tests, and am just playing devil's advocate. Seems though that people are jumping all over a product for no reason.
1. Why not multi-channel? Um, most SACD players out there (especially those catering to rich audiophiles, who seem to be the main ones even worrying about SACD any more) are only 2 channels. Most rich audiophiles only use 2 channels.
2. Why $3000? Related to above. Don't freak out over a $3k player from Marantz. Go to Audiogon and freak out over those ones. And note that they are almost all 2-channel as well. Think how much the players would cost with an additional 3.1 channels!
3. Why only SACD instead of universal? I've personally had some universal players, and I would want none of them for a 2-channel, music-only system. Built for primarily video, the other functions can be annoying. DVD audio in particular is bad, since it has menu displays that are way easier with a monitor or something. Skip it and give me a simple music player. I am about to get the Oppo for the HT/multi room, but have 2 other universal players sitting in the closet rather than use them in my 2-channel room.
4. Why SACD instead of blu-ray (from review)? Catalog titles. It will be years until blu-ray is a viable option for building an actual library with things like classical music. There are a few tokens out there, mostly either operas or off-brand orchestral recordings. I have ~1000 CDs, and haven't the slightest fear that I wasted all my money on them because now I'll just want the blu-ray version. It will never freaking exist. SACD is what you've got if you want an upgrade (either resolution if it matters to you, or multi-channel sound if you buy another player).
I wouldn't buy this particular player. I would however buy a nice SACD player for somewhat less money. NAD seems to make a good one, and it's 5.1 in case I feel like moving it between systems. The Marantz isn't the one for me. But that doesn't mean it shouldn't exist, particularly as a relatively conservative version within a product category when compared to almost any other dedicated SACD player. In fact, it's well in line with the price and number of channels of Marantz's previous top-of-the-line SACD players. Diminishing returns? Most likely. Returns period? Well, maybe...