Welcome to the club - (I'm 47) - so I can commiserate with you. I too wake up mornings feeling like I'm 80. Working on an old car vs. buying a newer one is a personal decision. One thing you can do is lower your tolerance level for car problems. As long as you drive, cars will break down and need repair. That's a given.
When my friends ask me why I work so hard at home, I tell them that I treat it as a second job. After all, money saved is money earned. This work allows me to enjoy some of the finer things that my peers can't afford. I see little difference between myself, who works 40 hours a week and wrenches in the evening, and the person who works 60 hours a week and then has to contract others to work on their car or home. At least I get some enjoyment from my evening work.
Don't let the new crop of kids get you down. They're hocked to the gills with their posessions. Myself (and perhaps yourself) own everything free and clear. Should the economy get worse, guess who'll fare better?
95 E320 Cabriolet, 131K