Cadillac truly lost their quality around the 67 model year. Gone was all the brightwork, great interior styling, metal trimmings and tight fit and finish. The 69-73 interiors were very cheap feeling and bland as can be.
I should know after owning a 68 and 72 Cadillac's, the 68 was much better inside, even the paint was of higher quality.
But compared to my now 64 Cadillac Deville that I picked up recently, the 64 is truly one of the last "high quality" stylish Cadillac's IMO. It's a much better well built car than the other 2 by far.
The 70's Cads were "ok", they rode nice and were very smooth, but to me the 71-73's were the worst years for quality, the body rattled and the car simply didn't have that isolated feeling like the older Cads did. The interior was cheap crap, even the exterior mouldings was garbage quality pot metal, but granted the doors and hood felt like a tank.
Cadillac improved the cars slightly starting in 74-76, the interiors got nicer looking, more plush, and was better constructed. Overall though I would say if I ever was in the market for a 70's Cadillac, my only other 70's Cad I would ever purchase again after the awful 72 I owned would be a 75 Fleetwood Brougham with the rear seat footrest. To me that was the epitome of pure luxury. A Rolls Royce of luxury cars.
But after owning a few Cadillac's, none of them can match the ride, interior comfort, quietness, plushness, style, it's imposing size, and even quality than my 78 Lincoln Continental. The Lincoln is literally like driving on a cloud, it is so unbelievably smooth, isolated, and soft riding that sometimes I wonder how could anybody drive a car like this across the country and not easily be put to sleep, it's that nice. Plus everything outside of it, like the quality chrome mouldings, the grill, the fit and finish, the thickness of the metal, the door panel quality and seat comfort I feel blows away the Cadillac's of the same year. Even the pre 77 Cads. One issue I personally have with the Lincoln is although it rides and drives supremely , it doesn't have a whole of lot of ornamentation on the inside like Cadillacs do, nor is the drivetrain exclusively "Lincoln" but rather shared with other big Fords of the era.
I honestly would love to have a 69-70 Cadillac as it has one of my favorite grills, I actually rode in one years ago, that car was awesome!