Safety, comfort, power and emissions vs. economy and reliability. Which is more important?

I have a 1985 VW Golf non-turbo diesel that cost me $600 5 years ago. It gets 50-55mpg on the highway, still has great compression, doesn't leak anything, not even oil and hasn't given me any major problems since I've owned it. I have changed a few CV axles, an injector line, the thermostat a couple... show more I have a 1985 VW Golf non-turbo diesel that cost me $600 5 years ago. It gets 50-55mpg on the highway, still has great compression, doesn't leak anything, not even oil and hasn't given me any major problems since I've owned it. I have changed a few CV axles, an injector line, the thermostat a couple times trying to get more heat and a noisy front wheel bearing (which I have access to a press and did myself for only the price of the wheel bearing.) I also have a timing belt I want to put on it and I own two sets of rims, one with snow tires and the other with all-seasons. And that's it.

But on the other hand it has no shoulder straps in the rear, no air bags, no ABS and no air conditioning. The heater also can't seem to keep up in the dead of winter when putting around town. It's paint is also cracking and falling off and the interior is deteriorating. It does smoke some at full throttle, as older diesels normally do. And it's only rated at 46 horsepower I do believe.

However, I just can't seem to bring myself to replacing this car. I love it and I can't seem to find a replacement car that appeals to me. I kind of have narrowed my search down to a Gen 2 Prius, a newer VW diesel or a 2014 Mitsubishi Mirage. I don't really want to spend more than $10,000 or get less than 40mpg. But I still am indecisive.

Should I paint the Golf and tack on a headliner and some seat covers or fork over the money on a down payment?
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