If my 3090 or mobo dies, for instance, I can send it to a repairperson and have a good chance of saving it.

While throwing out working things is terrible, the cost of servicing a motherboard outpaces the cost of replacing it. They can possibly still charge you 200 dollars and tell you the board cant be fixed, right? I think the right balance is that you observe the warranty period, try to troubleshoot it yourself --and then call it a day, unless you have a 400+ dollar motherboard.