O.k. my turn.
Here is what I did, maybe this will work for you or not but it seems like it applies so here it goes.
I drove the hell out of my car for the first 4-5 years, put every extra dime I had into it and had a good time. No regrets.
Then I got married and my outlook changed a little and not because of my wife. So I parked the car for almost 5 years and got my life in order. First I purchased a home, got married, finished my education, got my career going, started a family (which REALLY changes your priorities overnight), and then saved a decent amount of money to make sure my family is secure in the event business slows.
Now that I have completed all of that, I started putting money in the Mustang again. I drop money in it every once and a while for fun but nothing hard core, well not yet anyway.
The moral of my story is, don't second guess what you have done but have a set plan and timelines for the future, then stick to the plan. Maybe what I did will work for you or not. If you keep the car you can always work on it later when you get things in order. If you sell it you will always think "what if" ?
Hope that did not get to philosophical.