What should I do? 71 911E Targa for sale

[NGSmith]

I normally make my own decisions and dont post obvious questions but this time I think I need a gut check. I am looking at a 71 911E Targa for sale and it is a nice example of a semi original 911E. Here is my issue: While the car is a nice driver, I would want to take it to the next level and therein lies the problem. I think I could end up with more than the car will be worth and could be better off spending more for a car that is already finished the way I want but I could be wrong.

A little history on the car, the gentleman that owns it is a super nice honest guy that has owned the car since 1982 and has every record on it for every dime he has spent. It is a california car that had minimal rust issues (repaired in 82) and has all of the original drivetrain. He restored the car from 82-85 and has only driven it a couple of thousand miles per year since. He rebuilt the engine, trans and over the years has maintained and kept everything working properly. The car while it looks nice is aging and could be driven and kept just like it is for a nice driver or restored again to perfection. It has had a color change from Irish Green to Metallic Gold and while it looks good from a few feet, it would be ready for a change back to original. The left front fender has been hit at some time in its life and damaged the inner tub slightly but not bad enough to cause any concern. All of the original green paint is still in the trunk well so it was not that bad. It retains its original mechanical Injection which needs tuning as it makes for cold starting issues but runs great after warm up. Overall it is a very nice car for 21K but I am afraid that I will be in it much more than that to get it the way I want it. I think at that price it is a good deal but I am looking for opinions as to what a truly restored car would cost or be worth of this vintage.

Any help is appreciated. Attached are a couple pictures of the car.