What a great topic. So good I just had to register. I am a diesel shop owner also. At least that's what my business name says and how I market it. BUT.... that's not all I work on. If I did, I wouldn't survive. I work on just about anything. I found out fast you have to difersify to stay in the game.
Sure if I could have it my way I would just be working on diesel pick-ups and semi trucks. Instead I'm doing oil changes and brake jobs on the family mini-van. Don't get me wrong, I still love what I do (and I still make money at it), but it's just not what I invisioned my company to do.
Yes there is a special niche out there for the "diesel shops" or the off-road performance shops (which is how I advertise the business), but my bread and butter seems to come from the everyday maintenance items, ie: oil changes, brakes, tune-ups, window motors, diagnostics, wheel bearings, & ect. I'm sure you get the point. Oh, and most of those maintenance items are on the gas rigs my customers have not their "diesels".
Yes there is a market out there for a good diesel shop. I've had customers tow there pick-up truck a 100 miles for me to work on it because they know I will do a good job and they can trust me and my work. I even had a customer haul his Toyota 4 runner with a diesel in it from PA, because he said he could find a shop to work on it, but that's for another story.
My point being, you can be the best and only shop around with a niche, but sometimes you will have to take those smaller jobs that don't profit has good just to stay in the game, but in the end, it all pans out the same. Whither you do 5 jobs for $200 a job or one big job for $1000. Being diversified is the key.
That's just my 2 cents.