I would say that from the perspective of a classic car, that is fairly reliable and gets good fuel economy, the 80 is the cream of the crop. It is the last in a long line of adventurously-styled cars from when GM was a style leader.
The 1998-2004 Seville has more modern driving dynamics, but it has a bland, lookalike quality to it. You have to look at the nameplate to distinguish it from the crop of luxury cars from this era. The interior is an underwhelming place to be, as compared to the comfortable, regal command post in the 80.
As for engineering, I doubt the Northstar, with its two-piece aluminum block and complicated valve train will last as well as the 6.0 Liter cast iron unit with its simple and proven technology.
I doubt the V8-6-4 engine in those Seville's is proven. I thought they had real problems with that. As for the newer Seville the interior is NOT bland at all. Both cars have a typical interior of a great division of GM. To compare a vehicle from 1980 to something from the 2000's is a waste of time.
The 1980 had a 368 V8 that ran on all 8 cylinders and was one of the best.
The 80 California Seville had an Olds gasoline 350 with Port Injection.
The V8-6-4 is from 1981, and I am not defending that engine as anything but a curiosity.
The 1992-97 Seville is a groundbreaking design, but in 98 they rounded the edges and took the style out of that model.
The 80 is a classic car and it would be hard to compete against a new Cadillac in any other areas than exterior styling and interior quality.
Cadillac used a grade of leather until 1992 that is superior to what they use today. Your feet will disappear in the thick carpeting. The steering wheel tilts AND telescopes.
Compare the 20+ year old interior of any 80's Seville to a 90's Cadillac and you can see the difference in longevity and richness. The 90's model will be worn through before the 80's model is broken in. Unfortunately, GM took a hit in interior quality in the 90's. I know, because I also have a 95 Fleetwood.
If the uncompromising style and pure luxury of a classic Cadillac are what you desire in a smaller size with more modern handling and economy, the 80 Seville will not leave you wanting more. If you want a daily driver, this is not the car.
As the younger generation becomes older and becomes nostalgic for the 80's, the 1980 Seville will become even more collectible. While I love a 1960 Cadillac, there are few people who remember them when they were new or slightly used. They are now unattainable for a normal hobbyist. The '60 is beautiful to look at, but it doesn't handle well or run well with today's ethanol-laced gasoline. If a collector wants to get involved in Cadillacs, an 80 is a nice car that has some of that bygone magic, style and V8 grunt in a much lower price of entry. They get 20mpg highway and it is still possible to find an original example. The 70's Cadillacs have become bona fide collectors cars, as will the Seville.
What about the 1979-1985 Eldorado's. Another Cadillac collectors car in the making. I truly believe this is one of the most nice styled Cadillacs made. Especially the Biarritz version. I am surprised that they are not going for more money, yet. Although I did see a perfect Eldorado going for 10,500 in Santa Monica, Ca. I think the 1980 Seville and the Eldorado will be the last real collectors cars that will come out of Cadillac. I owned both and wish I did not sell them.
According to Richard M. Langworth (a major writer of automotive books) in the Illustrated Cadillac Buyer's Guide, speculates: "... it seems obvious that the low-production Touring Coupe will have a strong following among collectors ten or twenty years down the line... although these cars are still in the depreciation stage, and it's difficult to say when they will bottom out in value and start rising."
Nonetheless, it seems inevitable that they will begin to appreciate after a certain point, and that they will become legitimate collector cars somewhere down the road. The only question is when.
Moral? If you have one, keep it. If you want one, buy it while you can get it at used car prices.
This was written in the early 90's I think.