I was just in the same/similar situation, and did indeed opt to get a new 85D in replacement for my 85. My motivation was wanting dual motor AWD for winter here in Ohio, and wanting to get the Autopilot features that my first car lacked. I actually had purchased my 85 just in December as an inventory car, but overall my car and yours were QUITE similar. Option wise my '14 S 85 was the same, but added pano roof. And my car only has 5,500 miles...
That being said, my trade-in value to Tesla is almost $74k which is just nuts! That made it a no-brainer for me, especially since in Ohio when buying a new car you only pay sales tax on the delta. So for me trading my car in against the new car saved me 8% on $74k or almost $6k! Had I sold it outright I doubt I'd have gotten as much easily.
If indeed my trade value would be similar to yours, then even adding for extra mileage and no pano, your car should still be at $70k or just above. Keep in mind too that you may be able to find an inventory car (my 85D was a Chicago inventory car with a $6,500 discount). That plus the $7,500 tax credit adds in to make it a sweet deal. Of course the tax credit would apply even if you order a car. If the numbers make sense I say go for it... you might enjoy some added new features!