There is no data either way. It does not seem to make much difference either way from everything I have ever seen on the subject.
Spin down or leave spinning- both seem fine. I would not worry about that. Lots of other reasons why HDD's fail, so it's not likely to matter much.
Power consumption was not 18 watts. Who would believe that ? It was for the array, not the single drive in idle mode
RED drives and GREEN drives do about 4-5 watts each HDD. About the same as Hitachi 5400rpm and Seagate NAS or 5900rpm drives. A watt of power is nothing. It means nothing. Unless one HDD is half or double the power consumption of another it's not likely to matter much at all in a typical consumer set up (less than 20 HDD's)
1 watt x 24 hours a day = 24 watts x 365 days = 8760 watts. That is 8.7 kWh's. 8.7 x .08 cents per kWh = $.70 cents a year. If a hard drive is $5 cheaper than another but uses 1 watt more, it's very likely that you might not recoup the extra $5 you paid for the lower power consumption HDD before the HDD fails or the warranty runs out. Chasing power consumption is good to break a tie between two HDD's if that is what is important to you, but it's not worth spending more money on IMO. It's basically the same story on performance, it's good to break a tie on two same priced drives if that is important to you, but not worth spending tons more on generally speaking.
Hard drive is a hard drive.
The idea that RED drives or "NAS" drives will last longer is pure marketing aimed to get you to open your wallet. A GREEN WD or a normal Seagate is likely to delivery the same life expectancy and performance. The review that took apart the RED and GREEN basically found no difference between them except for firmware differences. (RED has TLER and Head parking disabled for RAID support)
In a normal server or desktop environment they are basically the same thing. The extra warranty on the NAS or the RED might be worth a little extra, but it's each individual's choice how much that is worth. To me one more year warranty is not worth $20+ but might be worth only $10. Others might disagree. I've seen some pay $35+ for the RED for no apparent reason, so while I personally disagree with that I guess it makes sense to some. Careful about marketing, HDD makers have been claiming higher reliability and all sorts of claims for 20 years and I have not see any change in reliability. If anything warranty times have gotten shorter (they used to be all 5 years).
If I save $20 each HDD and buy 5 drives, That is $100. I can likely buy a new HDD that is double the size with that money in the future. I prefer to keep the $ in my pocket until someone proved to me superior performance or reliability worth the premium.