I left the active duty with 15 years service. I work for the government as a GS 13 and sold back all my acitve time.So I essentially have 16 years fed service instead of one. I'm also in the guard and my active time still goes toward my guard retirement . My 15 years also goes toward my vacation time so I get a 26 days a year plus 3 weeks of military leave to fullfill my gaurd duties
The fact that it is a GS13 step one doesn't mean you can't negociate a higher step. It happens all the time, especially if you have the experience they want.
Being in the system is a pretty good gig. The nice part is you can establish some roots and not relocate e very three years.