Not $500 better. Although the price the seller is asking for the Fender is very fair, based on current market values.
It's been a while since I've played a Precision Junior, so I obviously have not played it side by side with my Mini P, but as far as I can tell they are basically the same bass. I play flats and am not wild about string thru bodies and I prefer to have a tone knob, so for me the Squier is a better bass.
Are the fit and finish, wood and components better than what is on Mini P? Probably, but any Fender Precision Junior you find will be at least 15 years old with no warranty. Modern manufacturing techniques have allowed for much better quality control of budget basses, so the Squier may well be put together as well as the old Junior.
In any case, I used to GAS hard for a Fender Precision Junior, but the Squier Mini has scratched that itch. I would not be surprised if the values of the Precision Junior drop a bit.