My thoughts are that I lean towards fixing the car.
It is not worth much as it sits. You might get $3K, $4K or maybe more for the car but you'll not replace it with anything comparable for that amount not even if you add to it what you would have spent on the engine.
BTW, my advice -- just so you have fresh numbers is that you contact salvage companies that specialize in Porsches to see what you might get for the car. Give Oklahoma Foreign a call. There are other companies, too. Consult the ads in Panorama and Excellence for their names/phone numbers.
Anyhow, you sell the car and that's that. It is a clean break. You get rid of the car and can move on.
OTOH, as I touched upon above you will not be able to replace the car with anything like it for what you get for the car and probably not even for what you get for the car combined with what you would have put into the car getting it back on the road.
With this $4500 engine your trusted indy suggests the car is whole again, runs again, and you have a very nice car to use again.
As mikefocke touches upon, there's an argument for while the engine is out of the car doing the AOS, plugs, coils, water pump. OTOH, you might just cut this down to say the AOS (unless the AOS looks fresh).
For the plugs, I would probably replace the plugs unless they were (like I said above about the AOS "fresh", clearly so to your mechanic's satisfaction). At the same time he can make a call on the coils.
And the water pump is certainly accessible to at least carefully inspect. The pump cost is not much though so it depends upon what labor costs.
But if the water pump shows signs of fluid leakage or a wiggle test finds play, then replace the pump and t-stat.
Same goes for the idler and tensioner rollers. Check them for excessive play or roughness. Replace if the need to is obvious. Or you can leave them in service: they are not hard to get at/replace if they need it later.
My thought is then to fix the car. Spend what you must, but no more.
You can throw a lot of preventative parts/work at the engine and the radiator springs a leak, or the fuel pump quits. Or you throw nothing at the car and the coils misfire or the AOS craps out the next run around the block.
So no matter what you do or do not do, you have to steel yourself for the possibility that something will come up.
Best of luck in whatever you decide to do.
Sincerely,
MarcW.