AP2 is going to be great but it isn't great yet. I think AP1 still offers all, perhaps more than AP2. AP2 doesn't read speed limit signs yet. It shows us the speed limit stored in the database, usually right but not always right.
If you have an AP1 Tesla, you've already taken the AP2 depreciation hit, I'd wait. They are getting better all the time. When you buy the next one, you are frozen in time with your new car while even newer ones continue to offer new surprises. If you already have an S, you get to drive an S, your AP is currently just as good, and you still get to wait and see what the new things are as they are released. Life doesn't get better than that.
The cat is out of the bag with AP2, that value drop has already happened to you, it's not going to happen again. You may see another drop for other reasons but even then it won't be as much as if you hadn't taken the AP2 hit first. I don't think you'll save much replacing now as opposed to later. I don't think you'll save anything.
If you look at cost of ownership, there are a lot of ways to calculate it. One way would be cost per mile driven. Since your car has depreciated, as have all our cars, the cost to drive it a mile is less than if you get a new one and drive that one a mile. So what would you get for the increased cost of driving it? You'd get AP2 which isn't a whole lot different from AP1. If it's a 75 or 75D, it'll be quite a bit quicker to 60 than if built a month ago. That'd be neat.
I don't know if all this is important to you. But you asked for my advice so here it is. If it was me, I'd wait. After all, you'd hate to buy a car with AP2 and then find you'd just missed AP3. As for me, I think I'm going to wait for the P150D with AP4 and 0-60 in sub 2 second "plaid mode". And then I'll wait a bit and look for one with about 8000 miles on it... maybe yours.
Best,
David