I found myself in a comfort zone but in an industry that was changing ( and declining ) fast. In a way I was lucky in that due to contacts I was offered something pretty different. At the time, ( I was 26) I got all the comments about lowering my conditions etc. Thats some time back now ( a lot f time!!!) and after a few career tweaks I am now in a job I really enjoy. OK so I was lucky but its a big world out there with lots of new things to do.
With the luxury of hindsight I would say that if you have a 10 year plan with some idea of where you want to be ( family, wage, location etc.) it makes it a lot easier to plan. As you get older you also make relationships with other people who open doors for you.
Never an easy call but the fact that you have made the post suggests this is the way you want to go.
If you can afford it, leave your present job on good terms and go for it. You can always go back, but with better qualifications.
isnt an option in my book!