A pile of out-of-date computer components is significantly less valuable than an out-of-date but working computer. Trying to salvage parts from old computers is only cost effective when you have comparable models still in use which you want to keep spares for - and even then, it's much simpler just to keep the whole machine. Regarding the specific things you're thinking about extracting....
Along with PSUs, the most common thing to fail on PC. Both degrade gradually over their lifespan, therefore should be replaced with new units
Really? How much do you think these cost? And they wear out too
OK, maybe, but since the connectors, speed and other properties change regularly, out-of-date memory will only work in out-of-date computers
Either keep the whole computer or give the whole, working computer away (there are lots of NPOs who would be glad to take them off your hands without the problems of WEEE)