I have been serving in the military for almost 15 years.
I have a BS in Buisness Management and I am almost finished with my Masters.
My degrees have helped with promotion but more importantly have made me a more well rounded and educated individual.
Many jobs that pay over 60k a year will not even let you in to do an interview without some form of degree or certification. I understand this depends on the field, but most higher paying jobs want experience (with) education.
I don't want to start at the ground floor and work my way up, but rather get another job once I retire from the Marines that pays similar to what I make now.
Your field is unique. My buddy was in the Navy for 12 years on Nuke subs and got out and makes almost three figures with no degree. Sure, they are closing his plant soon (because nuclear power scares the masses), but I am confident he can move to a different plant later. He is working on his BS because the plant requires a degree for upper management positions and that is what he is working for.
Sounds like you have a great gig, but I would not consider your situation the norm.