I'm in the eatont9999 camp on this. I think it's neat to be able to still enjoy the luxury and innovation that was the benchmark for the automotive world 35 years ago. While not comparable to modern vehicles, the amenities and technology employed by those crafty Germans is pretty trick stuff and keeping it functioning several decades on is an accomplishment.
Now, it's easy for me to tell other folks how to spend their money and time on these old cars
but I understand there is often limits to both the money and the time required to properly sort them out and have no issue when creative solutions need to be employed. For a real how to on some of those creative solutions, including manual window & climate control conversions, I highly recommend Squiggle Dog's epic thread on his Custom 300SD project. He's done some really clever and nice work to his car.
http://www.peachparts.com/shopforum/diesel-discussion/282304-my-custom-1980-w116-300sd-project.html
One last thing about the automatic climate control. When it is properly sorted it can and will work quite well and provide many years of flawless service. It's a real Rube Goldbergian contraption that was initially designed for the Chrysler Imperial and is worth studying up on if you plan on keeping it running.
Best of luck if you decide to purchase the car. Of course you will have plenty of resources to draw from on this forum and since you and I are both in Atlanta I would be happy to make myself available to lend a hand should you need it.