Even old designs on new semiconductor processes would be an improvement - a 3 generation old flagship card will be a bit cheaper to buy but will still have significant power consumption (ergo noise and heat) relative to the current generation.

They still work, until they don't because the vendor stops supporting them.

I've yet to see a graphics card which stopped being supported in reasonable terms. Except if you count 3dfx or other really old stuff, at which point it gets silly. Or awesome, guess it's kinda retro by now.

Opencl is not supported on IVY BRIDGES anymore for example, although there is no technical obstacles to provide such support.

Businesses would NEVER buy used cards. The are inefficient in terms of energy consumption, you never know if they were abused for mining and such, no warranty etc.

Parent didn't say "used" at all.