Well, this is it: you don't have to trash the preferences. The bug is not in the preference files, it's the EuCon connection (2.7.1). Even without a session opened, if you have the EuCon active, it crashes on quit.
Workaround: close the EuCon program BEFORE closing Nuendo.
Nuendo 6.0.x / Cubase 7.5.x
Mac Pro 3,1 Octo 2.8 Mhz, 8GB RAM, OS X 10.8.4
RME HDSPe, UAD2 Quad, 6.5.2, Novation Nocturne (as MIDI device), Unitor 8 (x2), ESI Pro MIDI, Blackmagic Intensity Pro
MacBook Air 4,2 4GB RAM, OS X 10.9.2