The initial startup costs might be high but if you think about it how often are you going to be changing pumps and radiators?
Generally the cpu blocks have been interchangable so one of those should last a couple or more years, the exception to this rule has been the i7 series. For me peace and quiet is worth the money and also the reassurance that I have nothing in the case that is seriously warm. Lower temps and more gradual temp buildup = longer component life. I've never had a cpu or gpu go since I converted to water cooling around 5 years ago and I generally overclock a bit, free performance should be used right?

The biggest expense these days are the all in one graphics card blocks which is understandable since they are using more power with every generation with the associated heat and noise.