I'm still waiting on mine, but it definitely sounds like a device that is quite different in function from the other new devices of the past decade. As you said, it's not something you play with for hours. On this MacBook Air or my iPad Air, you can browse the Internet, play games, write papers, etc. You can do a lot of that on the iPhone, plus it's more portable and can be used to give the other devices an Internet connection when you're away from WiFi. That's something I don't think a lot of people at work know about when they try to hunt for WiFi when out, or maybe their plan doesn't offer it for free.
But I can tell you where I think mine will come in handy. I have an iPhone case that doubles as a wallet, so it's thicker than most cases people have unless you get into Otterbox territory. You have to actually flip the case open, so there is a little "effort" into looking at the phone. Also, like today, I didn't take my iPhone outside with me today when I was doing some yard work because I was wearing shorts that had kinda small pockets.
So this is where a watch could come in handy. Assuming I'm still in WiFi range, I could've left my phone on the deck while working out in the yard and gotten my steps counted and been notified if anybody called. Same thing in the house or at work -- my phone could be on a counter somewhere and I would get notified of any emails, texts or phone calls with something attached to my wrist.
I also think with it being a new product without much third-party development behind it, it will take time for apps to come out that really make it worthy. The iPhone didn't get an app store for a couple of years. But slowly over the years more tools have been opened up and you've got some really awesome apps. I can't imagine school without Notability syncing between my computer, phone and iPad. I mean I can imagine it since that's what I did the first time I got a degree, and man it's much better now.
So OP, if you have buyer's remorse, return it if you can or sell it on eBay. I doubt you'll lose much money. I'm personally worried about spending $600 on it, so I might be in the same boat. But the above features I've just heard about make me think I'll like it.