The number of overclockers is pretty minimal despite what it seems like on these forums (on the order of less than 0.5% last I saw). The 7700K was a nice upgrade on its own vs the 7700 even if you don't overclock. 16.7% faster base (guaranteed worst performance) and 10% faster turbo for only 12% more money. Or in other words, a small but noticeably faster computer for the cost of a cheap night out.
I don't think that just because one core can reach 4.5 GHz that all cores can be assured to reach 4.5 GHz. That is a bit of a stretch since you could conceivably have one core that just isn't as good as the others. It just happened to be with the 7700K and 7740X that Intel has the single core and quad core turbo values almost the exact same. So with those two chips, Intel has already binned out chips that have differences between the cores. But that isn't the truth with other Intel chips. And it will be less and less the truth when you get more and more cores (the chance that one core isn't up to snuff increases with more cores).
I actually would love to see a massively high turbo. It'll be great for the short burst tasks that seem common in everyday typical computer use. But it would not be sustainable for very long. No problem with that as long as it goes back to a high base clock.