I'd say, do a stint in the reserves, and work on whatever cars you want, don't make working on cars a monotonous job. Dictate the jobs you take. I know a guy who does basically that. He's a Captain in the Army Reserves, and only works on Ducati motorcycles when he has the time. He runs the business out of his home, built a nice shop attached to the house to handle the bikes, and does a few bikes a week. He also teaches various classes through the summer on how to work on your own Duc, runs a webshop for Ducati parts, puts out an occasional e-magazine called Desmotimes and has a blog about Ducati bikes.
All in all, he brings in a lot of money between it all, and he doesn't devote his life to any one thing, so I guess it doesn't become stale.