That's a nice looking old rifle.
Aftermarket mags do not add value, and at least some of the one's pictured are.
Is the gun with a 5-rd factory mag worth the $500 asking price?....maybe...if you want an older blued Mini-14, and if you want that particular variation, and if it is in excellent mechanical condition, and if you accept the fact that those old Mini's aint scope friendly....and of course, if you want it badly enough,......but that's a lot of "if's".
Me personaly, I'd keep saving my money and buy a new one.
DGW