Here's what you have to do :
Go out to the garage, start it up and move it around. Sit in it for a bit, pull it out into the light and take a look at it. Pop the hood, look at it, then crawl underneath and look at it. Check the interior, then take it for a spin if you can. Get an idea in your head about how much it would cost to fix up nicely, then figure out if you have the time to put into it, and the money.
Park the car, leave it for the night. Have a few drinks, whatever. Through the night you'll think about it, what has to be done will sink in a bit. The brain processes everything at night, things that you didn't notice consciously will pop out.
The next morning go back out and take a look at what is bugging you about the car. Look into it really deeply, see how much you need to do to rectify the problem(s). Think about it for the next day or 2, talk it over with a few friends.
Only then can you make a decision. That's what I do. I look, spend a bit of time to let things sink in, take a second look, let it sink it, then a 3rd. If it looks no better or my view hasn't changed then something else has to change.
Be realistic about your decision. If you don't make a lot of money and see the car being a huge investment you might be better off selling it and looking around for another in good condition. They do pop up randomly from people who only see it as old crap, its how I got my 1st one that was close to mint.