The drive I have a WD blue 7200rpm from 2012...that is what my watt meter says when I hook it up to a power cord by itself. HDDs havn't changed much. Even an older SATA drive, about the same.
And, yea, WD red, 5400rpm drives....wow, didn't know they were that slow....i only use 7200rpm or higher. The tests in that review, very informative. Not up to my performance standards. No wonder they are so power efficient.
That sounds like access power consumption. The Blues, IIRC are rated around 6w idle and 9-10w access.
My Samsung F4EG are 4.8w idle and around 6w access. I can verify that the consumption on my server goes from 21w with drives spun down to around 31-32w with the drives idling, which is 10-11w, but figure only around 60-70% efficiency on my PSU considering the very low draw. It only goes up about 1w or so streaming over the network. For a pair of drives, around 10-12w total.
Anyway, I think that is a bit of a red herring saying a thousand dollar dedicated NAS to replace that computer. Only if you are talking a very high end one or something like a 6-8 bay NAS. Even a fairly nice 4 bay NAS is only going to run you in the $400-500 range. A nice 2 bay is going to run you $250-300.
If the difference is 30w even, that might only be 6-8 years to save the power costs. Or if it is closer to 50-60w, 3-4 years.
Or if you are looking at a low end NEW computer versus buying a very old one, or even repurposing existing really only gear...$150 for the low end new equipment can be recouped in only 2-3 years possibly. Maybe even sooner.
Same thing with repurposing old networking gear. It CAN make sense, but it depends on what you need. I see a lot of people talk up buying ancient first generation gigabit cisco and HP managed L2/L3 switches when the person needs a semi-managed or even unmanaged 16-24 port switch. Sure, that old Cisco switch only costs $50 and a new "off name brand" semi-managed 24 port switch is $150 new...but that new switch uses 10w and the old Cisco switch is using over 100w. Thats less than 2 years before the new gear has paid for itself.
Power consumption might not be much of a consideration in a gaming rig or something else that isn't operated very often, but something that is on 24/7 or at least most of the time it makes sense to consider power consumption as one of the elements when determining things like total cost of ownership.
If you need a really capable machine and a low power one won't cut it, then it doesn't really matter. If two machines are of equal capability for your intended use, then take power consumption in to account as part of the total cost of ownership, because one being $50-100 cheaper might not be if over even just 3 years it is costing $30-50 more per year to operate.
As for your friend, most people are going to miss $3-5 or even $6-8 a month in an increased electric bill unless they are paying close attention. Especially if you have electric heat or AC as month to month variation in temperatures can easily hide something like that...but it doesn't mean your bills didn't go up.
I am not personally advocating a NAS unless you need specific features it offers that a full file server wouldn't. I do advocate one if you don't want the support or complexity of rolling your own gear, which a lot of people don't want. I personally enjoy it though and between hardware selection, skill and OS selection and needs, there isn't much maintainance for me other than initial setup of the server and it can do things most NAS can't. For example run my Calibre server, plus iTunes server...but I can also schedule back-ups from my machines to the server, then auto-update my iTunes library with any new movies, easily run downloads on the server and a whole host of other things. Some of which some NAS can do (if not as well), some of which no NAS can do (I am not aware of any that can run Calibre server). Down the road I am probably going to move to slightly more capable gear (probably an i3) for things like Steam streaming to my tablet.