I've been pondering the same question, I also have a N5. At this point I'll probably wait for the 2015 Nexus or perhaps a Google Play S6 or M9 (assuming they happen). My reasons are as follows,
1) There doesn't seem to be an N6 compatible dashboard QI charger. I currently use a Lerway Qi charger with my N5. There is at least one comment on Amazon that says it's not compatible with the N6 (the clamps press on the volume keys and the QI sweetspot of the N6 isn't positioned well for the Lerway charger). If a Qi dashboard mounter becomes available for the N6 I'd start considering it again, but without one it's a non-starter for me.
2) It's still unavailable most of the time on Google Play and I've only seen it at carriers with terrible networks, T-Mobile and Sprint. It's not available at AT&T or Verizon. This is a signal that something is terribly wrong. It's a middle aged phone at this point, if they still can manufacture it three months after it was announced then either they don't want to sell any or they can't build them.
3) The Snapdragon 810 phones are around the corner. If I'm going to spend $700 then I want the very latest and greatest specs (even it they don't really matter). Both the S6 and the M9 will have the 810. Buying a locked phone from a carrier or putting up with TouchWiz or Sense isn't acceptable but if either is offered in a Google PLay Edition then that's a different story. The 2015 Nexus will almost certainly have an 810 and maybe it will come from a manufacturer that want's to build more then 10 of them. There was no shortage of the N5 so I'm assuming the N6 is simply a failed program which they will address in the next phone.