If your Intel® NUC temperature increased 5°C more than used to be, that will not be a problem, 40°C when your system is idling is normal and perfectly fine, the temperature in your system is not an issue, Windows 10 has more applications and information that requires more performance and that could be the reason that your system temperature increased a little more, but in this case you will not need to worry about that temperature you're seeing there.
And about your hard drive, it depends on your hard drive manufacturer but I would recommend trying maybe a firmware update for your SSD.
Sorry for a really late feedback, I'll go ahead and quote myself here "It is not a big issue". With that I of course meant it is not an issue that affects anything. I just wanted to report it. It seems as you say that windows 10, like windows 8, is more cumbersome than windows 7.
About the hard drive, not sure how the SSD could affect the HDD. Anyhow this has been reported from users with various systems so it's definitely a windows 10 issue.