The answer is, it depends, and much of the following is just my opinion.
First, what are you planning to do with the Xbox One? If you're just going to be playing games with it, I don't think the Kinect is worth it. Not many games support Kinect and with Microsoft no longer making it required you probably won't see a lot of support in the future either. The only time I use Kinect while gaming is to say "Xbox, record that" to save a clip when something amazing happens, but you can accomplish the same thing by double-tapping the Xbox Button on the controller.
If you're going to be using the Xbox One as a streaming media player as well as a game machine, the question becomes more interesting. I find it very convenient to be able to say "Xbox pause" or "Xbox volume up" rather than reaching for a remote; in our house we use voice commands constantly when watching TV or streaming Netflix. But this experience is only a good one if the Kinect understands you, and that depends on how noisy your environment is. The Kinect filters out sounds from the Xbox very well, but it doesn't do nearly as good a job of filtering out other people. If someone in the room is having a conversation and you try to give commands via voice, Kinect can have a hard time understanding you.
Therefore, my opinion is that if you're going to use the Xbox One for TV and streaming, and you either live alone or with one other person, then the Kinect is worth having. If you have a big household and there's often a lot of people chatting at once, the Kinect might struggle to understand the commands you give it, which will lead to frustration.
Also for what it's worth, I find the gesture commands to be not only useless, but annoying. Far too often someone will reach forward to grab a drink off the coffee table and Kinect will think they're trying to do a gesture and suddenly the gesture UI pops up on screen.
Now all that said, this November Microsoft will roll out an extensive update to the Xbox that brings, among other things, Cortana to the console. Currently the only way to give voice commands to the Xbox is via Kinect; a headset microphone won't work. Cortana could make Kinect a lot more compelling, or conversely Microsoft might start supporting microphones other than Kinect for voice commands. We'll have to wait and see how that plays out.