When you find a new Intrepid for $5K, let me know so I can get one too. More seriously, though, it depends on just how much you like the car that you have, and how good of condition it is in. Is it worth spending the extra $3500 on? Could you get a decent Intrepid for $5K? Even if you could, you still don't know what is wrong with it, what kind of repairs it is due for, and how the previous owner(s) treated it. I would probably stick with the Intrepid that you have now, and fix what is wrong with it, rather than buy a different one and have to possibly end up fixing a whole slew of problems shortly thereafter.
I agree, if go out and spend 5 grand on a used car that you know nothing about I think your asking for trouble. I would spend the money on the suspension and then look for the best deal on used body parts and shop around for a good price on paint work. That's a great looking cat you have.