Front rack symmetry - spacers and handling The combination of disc brakes and full mudguards on my tourer means I'll need to space the left lowrider rack at least 30mm from the fork. On the right I'll only need 5--10mm. Should I space them equally from the point of view of handling? 

The panniers for the first trip will be fairly lightly loaded and will be different: one will be my Altura Morph that converts into a backpack because I'll need a backpack when I arrive; the other will be a slightly fatter roll-top.

I've already got the rack, having used it on my hybrid. With a single front pannier the handling was awful at low speeds (but I also had a child on the back) so I'm wary about getting it wrong for a longer ride.
No, use the minimal amount of spacer possible. Having to space them out at all is a necessary evil and introduces risk of the bolts loosening or getting bent/broken. That risk far outweighs any upside of making them symmetrical, because spaced out rack bolts having issues like that is a real thing that happens. You probably won't be able to notice any handling differences from this much spacer regardless, but if you did you could negate it by packing slightly less weight in the more leveraged side.