It depends, I'd say it's worth if you own multiple iDevices or Macs for that matter, and you are willing to spend a few weeks learning how to tweak the server to fit your needs,cause setting it up locally its not that hard, but outside of the network that's when it gets "funny", you can handle as much users as you want, like I said, if it's local network you won't have much problem. other than that, I don't see any sense of owning one.
Or maybe you could get it just so you can have a second drive, without doing it yourself and avoid warranty.
I myself was lucky enough to get a brand new, not refurbished of the 2011 model for half the price, and so far I've been researching online how to tweak it, cause trust me its not that intuitive as apple promotes,( i ended up wiping the hard drive and doing a clean install) but the profile manager access is worth the effort, that is like I said if you are planning to manage all your devices.