Here are my opinions
1) $39K for a 70D is way too high. If it was closer to $25K with no issues in perfect condition, then maybe in this market. Regular/normal market, I wouldn't even consider it if it is anything more than $20K.
2) I would stay away from 70D/70 model. They are using the same cells as the 85D/85 models which tesla neuter the charging speed. Some might got a bit back after some updates, but I think it is still drastically below what they got originally. Compound the issue of a lower voltage pack, you are essentially looking at a 60D/60 charge speed. Remember those?
3) if range is not an issue, then the 70D would serve you well and assuming you transfer it right, then you should get to keep the free unlimited supercharging which if you use plenty of, might save a significant chunk on the lifetime cost of the car***
4) *** here is the asterisk point. Be prepared to cough up a hugh battery replacement cost. The numbers floating around is $15K-$20K for a new pack. Now it is wholly possible you won the lottery and never need to replace your battery pack way into your ownership of this 70D, but I wager most people don't win lotteries. Time/battery age is the major issue in your case here that will most likely kill your pack, not vehicle mileage.
5) for $39K, why not look into other EVs which still have tax credit remaining which you can get at a comparable or cheaper cost? Think id4, standard range mach-e, etc. Heck if you believe the Democrats in Congress, why not wait for the renewed EV credit? Heck why not consider the model 3? There are a lot of options if you are in the $39K range.
6) The technology in the 70D is definitely ahead of most other common internal combustion vehicles, but compared to the newer EVs and definitely compared to a model 3, it will be feel like a car of the past. The Tegra powered MCU (Media Control Unit) is way underpowered for what Tesla allows you to do. Hence things are not always smooth or responsive. If you can put up with it, then I say you are good to go, but if you are expecting newer Tesla MCU response, then I say look elsewhere. You can always pay for the upgrade the MCU, but I hear that is at least $1500 or more for the upgrade so factor that into the cost.
7) Range is a tricky one. Remember Tesla tend to not meet their EPA range and definitely never meet their range they state on the gauge. I know because ever since I got my car in 2016, I have never ever got anywhere close to the range they promise even driving pretty conservatively. So if the Tesla says you have 200 miles, I would derate that to 80% to be safe if you are a normal driver. If you are an aggressive driver, derate that to 65%. Cold weather or towing? Make that 50%. So you might say you do not care for long range, but just be aware of your real range vs what Tesla's instrument cluster says.
Personally for me, I would stay away from older Model S mainly due to the impending warranty bill related expenses and old tech you are getting with the car. Teslas are cars you don't want to own out of warranty and you might still have some warranty left on the used 70D you are looking at. But I wager you can get a new Tesla Model 3 which will have a longer warranty period compared to your 70D you are looking at.
I recommend looking at other EVs if you are looking for EVs. But if you must stick with Tesla, I would say spend a bit more and go for the Model 3 Standard range. It is a decent car though you will have to call them to get the special price. If you need the space, pay quite a bit more, and get the Model Y if you are OK with with the looks.
Best of luck on your decision!