> in practice takes roughly 10 years for the savings to materialize... and by then, you've already swapped your CPU 3 times
Actually these days, not so much. I've got an i5 2500K that I bought in early 2011 in my home workstation, and I have no plans to replace it any time soon. My general rule is that I won't replace a processor unless it's both old and I will get around twice the performance of the old one. Looking at what I'd replace it with if I was to build the same machine today - an i5 6600K - there's just no point. I'd get about a 50% boost over what I have, and what I have is already more processor than I need for just about anything I do with the exception of gaming. And for that the money is better spent on a new video card, and that's what I do replace every 2-3 years.
In the past with Moore's Law that was around every 2 years, but Intel's been stagnant on progress for so long, they're now running ads like this:
Oooo... up to 28% better performance than a 3 year old part! And all you need to do is replace your chip, motherboard and probably RAM. Pass. Instead of spending $600 on all that I'll just drop $200 on last year's hot high end video card.