I don't think Infiniti made a grave mistake, I just think they let it go too long without divorcing themselves from the design and coming up with something better. The Pathfinder is actually considered a good all around truck, check the Edmunds SUV Comparison where it comes out on top.
Also, given the QX4's long list of luxury items which HID's is only one of them, such as in dash CD changer, leather/wood wheel, 17" alloys, Bose system, laser cruise control, and all-around better interior styling for less than the base model MDX. This makes a compelling argument for the QX4 when it comes to value for your money. You'd have the get the touring MDX and aftermarket parts which would put you over 40K for a QX4 at 36K to get an equivalent auto.