I bought my 78 , two years ago. I paid 15 grand for it. A lot of people say I paid to much, but I was offered 20 grand for it last Oct. It has most all the options Caddy could offer. Also has the level ride system. Mine had 11,500 miles on it.
I have seen this one, because I track 78's that are for sale. I know what they are asking for it. It is nice ,but it doesnt have as many options on it ,as mine does.
Ones that are loaded up to the max have been going for 12,000 to 20,000 dollars. That is if they are low low mileage cars.
This one probably would bring 8 to 10 thousand . I wish the guy had more pictures of it at his site.
TJ is right. Head liners can be a problem, but it only cost me 40 bucks for material, and a few hours of my time to replace it. I have not had any problems with the drive train. I did go through and do a tune up and etc...to fix minor problems.
Now that all the problems are fixed , I have been enjoying the car. It is a nice handling car .
Good luck to you.