because these end up generating most of electricity. older plants matter less specifically because these are less efficient - operating them means more fuel costs per MWh. normally, you can see new flashy plants generating all the time it's practical, because these are more efficient, have less maintenance downtime etc and when demand grows, progressively less efficient units start generating coming from spinning reserve. the two exceptions are NPPs which are best operated at constant high power because of their neutron physics and renewables that are literal free energy so everything they do is taken in. the only place where you can improve efficiency of NPPs is in turbine, and that probably is pretty well optimized unless turbine is very old, because increasing steam temperature would mean changed conditions in reactor in way that could happen to be out of spec. we have figured out wind power pretty well, and perovskites aren't a thing, and won't be a thing until they become more durable, which they won't. in all cases, upgrades would have to make sense both economically and/or in emission costs. this includes CHP and laying municipal heating grids, and good luck with that with how dysfunctional american local govts are (where probably biggest emission gains from CHP could be made)

you can redo this for other types of thermal powerplants and come to the same conclusion. if you say that saltman&co and his assemblage of lying machines can outsmart thousands of turbine engineers, you might be a shill for making other people believe that or a moron for believing that yourself