It's not a silly question - however - I'm not sure there is a simple, straight forward answer. I use hibernation and I've been running my DNS-323 for over four years, with one disk failure (and the disks were not new when they were installed in the DNS-323), so I'm not particularly worried.
Selection of the hibernation interval may play a big part - mine is set at 15 mins - however my DNS-323 is awake continuously for roughly 12~13 hours a day, and hibernates at night.