If I were hating my job at 30 with no prospect of things getting better, I think I'd at least ask myself whether maximizing my salary should really be my priority.
The more you can save and invest before you start the inevitable slide toward disability, the better. It hits many people earlier and harder than they would ever expect.
Having savings is a good idea in general. But that's not necessarily an argument for staying in a career you hate so you can make a bit more money. Maybe it's just a particular job. But people do also choose careers that end up just being a bad fit. If that's the case, you're probably better off changing horses sooner than later.