The Porsche 931 (ie, 924 Turbo) is a nice car, though like all 924 models it suffers an undeservedly poor reputation related to the 924 series having originally been designed as an Audi production model (and using many VW/Audi parts). As a collector car, it is unlikely you will see this car increase in value or stay better than a typical devaluation curve because the 924 is generally not desired by collectors (for reasons just mentioned). While this is not a reason to not want the car, it is important to understand when considering your purchase price and possible VCM II expectations with resale.

And while resale value of the car, and it's collector value will be low, repair costs will still be on the expensive side, related to the fact that this was a somewhat expensive item to purchase back in 1980. However, since the 924 series used many VW/Audi parts that were shared with other less expensive cars, your overall cost of ownership will be less than other 1980 Porsches. Turbo models of any car will cost more than normally asperated versions due to there being more parts and more stress on the engine. This should not be a major concern going in though if everything is in good working order to start with (even for an inexpensive car, it is worthwhile to pay for a pre-purchase inspection with a knowledgable Porsche mechanic... the most expensive Porsche you can buy is often a cheap one).

As for safety, it's a solid chassis and wrecked examples I've seen have ford vcm 2 faired well in some fairly heavy impacts. The basic chassis remained mostly unchanged from the 924 though the 968 of the early 1990s. However, it is not a modern car and will be lacking in features like ABS and airbags, etc. But for it's time, it can be considered a safe car.

Cars of this age are not especially complicated and most mechanics and hobbyists can do alot as far as working on them. Though there are enough specifics that are unique to Porsches where you would also want to make sure you have a good knowledgable mechanic.