356's came with +5° caster from the factory and are much more stable at higher speeds. If you NEVER (NOT EVEN FOR A MOMENT) drive your car above posted highway speeds then one could argue that increasing caster above VW's spec (about +3°?) isn't needed, but even 1 short blast down a straight road (hey, I'm just going to see what it will do) can go wrong. Many years ago I decided to see how fast my Cal Look bug would go down this long hill. Not having even stock caster (when I lowered it I knew nothing about caster) the car was 'a little darty', even at only 55-60 mph. The car got hit by a side wind coming down this hill at 105? 110? mph and was pushed into the opposing lane before I could react. I was very lucky that day- no traffic coming at me and no barrier in between lanes to hit. After cleaning off the seat I vowed never to do that again! I learned about caster shortly after and it's amazing what a couple extra degrees will do.
VW drag racers, before figuring out all this, struggled with keeping their cars from ending up on their roofs when it was windy at the far end of the track. Once guys realized what was going on and started building more caster into their cars the sport became MUCH safer.
I hope this helps. Al