I pre-ordered the Series 0 Apple Watch the day it became available.
I used it over the course of two or three months back in the Summer and Fall of 2015. I found that it could do certain things pretty well, receiving notifications, answering messages, taking one or the other phone call, I used it for activity and workouts and closed my daily rings - but after the novelty of it had worn off, it suddenly became a daily chore to wear it. I took it off, put it back in the box and put it in the drawer, where it still rests today.
I kept following the Apple Watch during the keynotes, but never felt a certain urge to buy one - until five weeks ago, when the Series 5 with the always-on display was announced. First I pondered to hold out until next year, but then my wife wanted one to better stay connected (for example not missing out on phone calls from kindergarten, where our daughter started to go this year, just in case). So I thought what the heck and ordered one, too.
Now I've been using my shiny new natural Titanium 44mm Apple Watch with cellular connectivity (in conjunction with a new iPhone 11 Pro) for almost two weeks and I have not regretted one second since spending the money.
The difference to the Series 0 is like day and night, the display is gorgeous, it is lightning fast, watchOS has been greatly improved, everything is working as expected, they have great watch faces and the whole experience of wearing and using it has been totally improved across the board in the last four years. I have a mixed use case of primarily fitness, activity and workout tracking, receiving notifications, sending and answering messages, occasional phone calls, emails and management of daily tasks. I also find the very accurate heart rate monitor, the ECG and the fall detection really useful.
I also like how it seamlessly switches between Bluetooth-iPhone, WiFi and cellular. The watch really feels independent.
And I am getting real great battery life out of it, too.
So from my point of view, as a former Series 0 owner and rejector, I would say yes - if it fits your use case and you can churn out the necessary money: go for it. I think there has never been a better time for Series 0 upgraders.