Not that there's anything wrong with the Adorama deal... there are plenty of Refurb D600s all over... What I have seen (I hate this thread because I'm feeling compelled to jump on a D600) is that there are a few reputable (at least 1) dealer that is offering a 6 month warranty instead of the standard 90 day warranty on the refurb...
Yes, but not with this lens. What I'm unclear on is if the lens is a throw-in or also a refurb. I got my package last year new for $1998 with the intention of possibly selling the lens and upgrading, but as I said, I love this lens.
For me, with Adorama I'd get 15 months (90 days plus the VIP plan year)plus an additional year from my credit card company. Nikon warranties the refurb for 90 days, and many dealers will extend it to varying lengths, as you note. You're always better going with dealers you trust and have heard positive reports from, and Adorama is one I'd put in that category.
As for the question of how much a Nikon warranty is worth, that really depends. In the case of the D600, with it's shutter issues, I'm very happy to have had the full warranty. As I mentioned, my credit card company adds a full year to any manufacturer warranty, so I would have no issue rolling the dice on the refurb/lens combo, particularly given that on the refurb the dust issue is likely resolved. But everyone is different. For me, there are certain things I prefer to buy new or "as new", and camera bodies are in that list. Lenses, not so much, provided I can buy in person.