I would expect the newer model Panda (with what amounts to Fiat 500 running gear) will handle better as they have 50mm wider track subframes. Simply slapping wheel spacers to a 169 will handle badly and won't look "that much" different.
Saying that, it's a short wheelbase car. Making it wider makes it less stable in a straight line.
Wheel spacers at the front will mess up the steering geometry causing bump steer. It will be especially bad off road. At the back, they probably wont have any discernible effect but are likely to stress the wheel bearings. These are not low cost on the 4x4.