First off, you have to admit they make a nice product - fast, smooth, comfortable, and beautiful (subjective).

However: They’ve gone the same way as Mercedes.  Lots of fancy high tech features, planned obsolescence, no concern for durability.

Their primary customer base is wealthy people who do a short term lease so they can always have the latest and most fashionable Escalade.  And corporate customers who also only care about a short term lease.

And like Mercedes, in 10 years most of their cars will be scattered across Russia in about a thousand pieces.  If you are a person who wants a long term relationship with a car, look elsewhere - lots of better luxury and near-luxury cars. 

Only if it's really cheap those are not collectors items at all and they weren't the greatest made vehicles. But if you like the style and it runs okay if you can get it cheap enough you can have it as a toy

If you’re asking if modern Cadillacs are any good (in terms of quality, durability, reliability), the answer is No.

The last really good Cadillacs were made in the 1960s.

GM makes Cadillacs, and the answer is no. They are plagued with problems.

Lacrosse is more reliable than the caddy. I personally would pass on both but out of the GM line up seems Buick is the more reliable side of that mess of a company. 

Avoid any of these newer GM vehicles especially out of warranty.  If they were brand new, I would have said to lease them (at best) if you really had to have them.  But now, out of warranty - just avoid them.

I Have Had This Question Should I Buy A 1994 Cadillac Seville 4dr Sedan Touring STS

What Do You Think Abouth 2015 Cadillac CTS And 2015 Buick LaCrosse

I would pass on both of those cars. They’re GM vehicles and their quality is junk. You could get a Lexus ES or Toyota Avalon as they’ll last way more. But it’s not the best time to buy a used car cuz prices are insanely high from the coronavirus, the gas shortage, etc.