Is it worth it? Only you can answer that question but consider this: with a GPS only version, you can do everything the GPS + Cellular version can with the exception of leaving your phone at home. And to your point, you can pull your phone from your pocket so maybe it's not for you?
My primary reason for purchasing Apple Watch was fitness and activity tracking. I work at a desk so it's easy to sit for long periods of time. Since having it, I've discovered that I really appreciate the notifications for calls, mail, calendar, flight information & tickets, heart rate, sleep tracking, directions, music control and probably a slew of other things as well. You can do almost if not all of those things with your phone but I appreciate the convenience and motivation the watch provides. When my phone is laying on my desk and I'm in another room it's nice to look at the watch to see who's calling and that's part of the premise of having a GPS + Cellular version. That said, I always have my phone with me when I leave the house so cellular is not necessary for my use case. The value is not there for me with the additional monthly and upfront costs--just my perspective.
Ultimately, it has helped me be more aware of my activity, heart health and has motivated me to get into the gym and for those reasons alone it has been worth it. The rest of the stuff I mentioned are the icing on the cake.
