FWIW, I bought a new Ender3 as a kit not too long ago, it was $150 IIRC. And by being forced to assemble it, I learned a good bit too. It might be worthwhile to watch their store & see if they put it up for sale again.

The only upgrade I’ve done that I really felt made a difference was buying an enclosure for it. Nothing fancy, it’s a fireproof bag over an aluminum frame. Even more than controlling the temperature, it also keeps it dust free when not in use - that’s probably the biggest win for me.

As for buying the used one - these things do wear down. Start by checking the feed gear & the PTFE tube. If the filament feeds well, then also check the belts, rollers, & nozzle. Those are really the common wear items imo. Perhaps obvious, but make sure the seller gives you a copy of the slicing software (should be free on their webpage) and also the little USB-A to Sim card doo-hickey that you need to move files back & forth.

I’m a bit surprised I’ve never heard of LONGTIME. Seems like they’re doing exactly what I’ve wanted - searching out products designed to last.

https://longtimelabel.com/en/

That said, not sure I need a Buy It For Life cable. Far more interested in BIFL appliances.

Mildly interesting, as I just did nearly the same, going from a GTX970 to a Radeon 8570. Did not have the same “it just works” experience however. But I blame that more on my lack of Linux knowledge than the video card.