I've seen many colleagues going from engineering to "MIS". Pays much better - at least here around my place.

Get the money and have a joyfull hobby involving mechanics, I'd say.

The choice is all yours since it is your life.

But to help you decide, I'll list some reasons for continuing in MIS. As bhescobar implies, MIS is a growing field that is attracting many engineers today. The salaries are very lucrative now since more positions exist than qualified applicants. The uncertainty is how long before a contraction occurs, and how deep of a contraction will happen. ME is an established field that certainly will never disappear but with so many automotive company layoffs lately, I suspect there are more experienced ME than positions at this time.

The obvious reason for getting the BSME instead is your interest in the field. It can be dreadful doing a job that doesn't interest you. But millions do it everyday. (Remember, people often consider "work" an obscene four letter word.)

Since you are in the Navy, you may not have a choice which field you can pursue.

Go for ME. The main reason I have enjoyed my ME career so much over the years is that the toys I get to play with are really cool...

You worked in navy and I am sure you must have had good experiences on topics related to marine engineering which is a sub sect of mechanical engineering. Salary structure in MIS related job is surely an attractive factor. However M.E is a versatile branch of engineering and its scope is generally uniform at all time. After obtaining M.E you can consider to specialize in environmental related subjects which are having good scope.