"Sipping power" is a bit of an overstatement. Sure, at 35W idle, they were very lower for the time but modern <10nm monolithic die CPUs are way more economically than the older 32nm, 22nm, and 14nm CPUs though. That can't be argued.
A 12th Gen quad core NUC CPU will use at full load what Sandy Bridge quad core uses at idle, while also getting better performance.
There's just no comparison.
A google search on benchmarks and tests.
The numbers I cited earlier were reported by the CPU's package power sensors which were in turn read by LibreHardwareMonitor.
However, painting with broad brushes, Sandy Bridge has modern power management and idles comparably to newer CPUs (a lot better than some modern ones even).
Also an old system is likely in a case that accepts multiple drives. That NUC is not going to have space for my 3.5" storage drives. Yes I could invest in NVME SSD's, but the point of this is low cost and using parts I already have.
I have 10+ old 3.5" HDD's laying around, if one dies I can easily swap it out at zero cost to me and keep my home server going.
We were just comparing CPU power usage. We're going off-road here and splitting hairs trying to cater to the needs of every enthusiast who builds his custom home lab.
Nobody's telling you how you should build your NAS or home lab, but the point about big differences in CPU power consumption across >10 years of progress still stands.
Sandy Bridge consumes that much at full load, but that can also be said of current gen processors (which incidentally usually go even higher).
At idle or low load, Sandy Bridge is plenty economical just sipping power. These aren't Pentium 4s which guzzle power like it's draining Texas of its all its oil even at idle.
My Sandy Bridge i7 2700K is sipping 10W at idle/low load right now, and that's actually lower than my Alder Lake i7 12700K that's sipping 15W at idle/low load. At high loads they go up to 95W and 150W respectively, which still comes out in favor of Sandy Bridge.