You make excellent points. I think the key difference for me when I got the NAS was that I wasn't replacing an existing system. That and I actually enjoy playing with storage and networking, so I'm able to cover most of those bases you mentioned myself.

For the power issues, you may want to look into getting a UPS (Uninterruptible Power Supply) for anything you want to stay powered. Larger ones can get pretty expensive, but you can usually find some smaller ones for a decent price that I think would be fine for small business use. I've used and had good experience with UPSs made by APC.