Whether to buy new S85D and sell S85?

If you're the type of person who needs the latest/greatest and has money to burn, go for it. Otherwise, it doesn't make much sense to me. Give it another couple of years. You never know what innovations are coming up that may make you want to repeat and rinse.

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!

You may get $70k for your car Steve, but not by selling on these forums. Just for instance, I turned down an inventory car spec's like your car, with Autopilot, for $83k. After the fed tax rebate, that would put me at $75.5k for one with less than 5k miles. I've seen CPO pricing in the high 60s. So you can probably get $70k for your S85 in the general public, but likely not by those who read the forums here. Either way though, I wish you the best of luck - I really do hope you get a great price for it!

Does it have the autopilot hardware? Lane keeping, collision warning, adaptive cruise? Or was it made before the tech package included that stuff?

I would suggest that you if you are selling your S85 that you get a nicely discounted inventory P85D. You are going to be spending a bunch of money on the switch and I'd rather use the opportunity for a noticeable improvement in performance. You can get an inventory P85D for around $110K if you look around as they are starting to be discounted about $10-15K. IMHO that is a great deal and only a bit more expensive than a nicely optioned S85D. Whatever you pay extra for the P85D you will likely get a bunch of that back later if you sell it.

I'm in the same situation as the OP, except my S85 is a 2013. My thought is that financially, the best time to sell my current car and trade up would be now, since the 2013 car is only going to go down in value.

However, I'd like to wait and see what improvements are announced along with the X, or at least late this year. I'm guessing they will improve the autopilot sensor package at a minimum, and give it more capability. AWD and autopilot were the two features I really missed when I bought my car, and I knew that I might not keep this one as long as I usually do (8-10 years).