As you said, there is not much in the way of direct financial compensation for having a PhD in industry, but it can act as a foot in the door and it can (depending on the company) mean you get treated a bit differently once you are hired. Researchy type projects tend to get pushed to people who are good at open ended researchy things, and having a PhD is a good indicator of that.

For me the biggest value from my PhD came from the writing up. It is really, really, really hard to get from having "done all of the work" to writing a coherent, well defended thesis on it. You will get very good at spotting holes in arguments (particularly yours, but also other peoples). You will get a very real understanding of how much work is involved in getting from 95% to 100% finished. It's not directly valued in industry but I know that I benefit personally from my writing up experience.

And you get to call yourself doctor. That's nice.

A PhD is required to do research in academia and most industry labs. Otherwise, it's a net loss. However, it's free and fun for a while (if you don't work for an asshole).

A PhD programme is ideally an opportunity to work on whatever you want, for years, in the company of smart people who are also interested in the same subject. You can use this time to try out different ideas and see if any of them take off. Having that shot is valuable in itself, even if you don't "succeed" with a research position afterwards.

Plus, sometimes new startup ideas, connections, or key skills come out of a PhD. The traditional approach is to found a startup directly from your research, but equally important is the role of PhD projects in helping you identify people who will get things done. If they flake out on helping write an academic paper, what will they do when you're working on a company?

Now sometimes a programme falls short of the ideal. You may end up teaching too much, you may end up working on projects you don't like because the funding is there, and so on. If that's happening, then that is a reason to quit. If you have an incredible opportunity that comes up and isn't compatible with continuing, that's a reason to quit. Just quitting because the grass is greener, though, does not seem like it will work.

I'd recommend staying with it. If you're young (i.e. straight out of undergrad), it'll seem like the ~5 years you have left is a long time.

As somebody who spent some time working and then came back, though, it's just a short hop. The Ph.D. will only open doors for you in the future, and the six-year commitment is not an easy thing to do the older you get, with greater lifestyle expectations, family situation, and the general crotechety-ness that comes with time.

It's easier to immigrate, as a foreigner to the USA/Canada/Australia, if you have a PhD. That's really the only reason I'm getting my degree.

Well I've heard that Apple won't even bother considering you if you don't have at least a minimum of a master's degree in something related if you're applying for the Spotlight team.

If you're studying something hard and you get good at it someone will want to hire you. You will have essentially paid for a good chunk of their R&D for them.