About the D600 dust issue, Nikon released a service advisory late last month:
http://www.dpreview.com/news/2013/02/22/Nikon-issues-service-advisory-for-D600
http://support.nikonusa.com/app/answers/detail/a_id/18180
Quote:
"...'removal may be difficult using normal measures' and advises customers who have exhausted conventional cleaning options to 'consult your nearest Nikon service center', whose technicians will 'examine the camera thoroughly, and service it as needed."
It appears the dust issue could still be present on some units.
I also have a D7000 and have also been pondering an upgrade to FF.
However, it's not as simple as getting a new body. The upgrade will also entail getting new, and more expensive, FF glass. I have a few lenses that would work well on a full frame body (28-300 zoom, 50 f/1.8, and 100 f/2.8) but I would definitely want to budget for new lenses.