I'm replying without reading comments, so I apologize if you've made a decision or I'm just repeating what's already been said.

Things to consider:

How long have you had it and when did you last use it? Relatively speaking, is this a long time or have you left a camera to sit in the past and then gone back to it down the road? What are your photography goals and will they perhaps change so that you might want to use the Nikon again.

Perhaps it's best to wait until the honeymoon with the new camera is over and see how you feel then.