I don't know if Sandy Bridge's time is up now, but for me it was up when 22nm IB was released. At least 22nm IB gave a decent power reduction for same performance over SB.
But this 14nm Skylake launch just has me puzzled (business-wise, not technology-wise). Its like 14nm gave Skylake no benefit over 22nm Haswell. All the performance gains are architectural, designed in by some hard working engineers.
In the meantime, 14nm looks to be basically 100% cost-reduction focused (areal shrinkage maximized, electrical parametrics be damned) versus 22nm and 32nm.
So here is my half-baked assessment at this point - Whether or not Sandy Bridge is made obsolete by Skylake, the progression of diminishing returns with Intel's Tick-Tock tells me, as a consumer, that I may as well buy Skylake now because there is pretty much no damn good reason to hold out for any future Intel processor(s) as they are also just as likely to deliver, at best, a solid 5% performance bump in 1, 2, or 3 years time.
Intel's Skylake is telling us that this is not as good as it is going to get, but at the same time they are communicating that 10nm and 7nm are going to give us CPUs that might be, if we are lucky, another 10-20% over what Skylake is giving us today.
Buy one now, log out of your Anandtech forums account, and don't worry about the semiconductor world for at least 5 years. Save yourselves hundreds, if not thousands, of hours to go do something more productive with your lives in the meantime. Maybe 5nm will come along in 2022 and give us a grand total of 25% improvement in performance/watt over Skylake, then its time to consider an upgrade.