This thread has been... interesting.
Providing the bushes and diff are in good condition, caster and bump steer are the main causes of the wandering feeling so many people talk about.
Caster can be good as it gives you dynamic camber, effectively something for nothing and extremely useful on track. However, on a road car, it's relatively pointless and the negatives can outweigh the positives. A little is nice as it helps the steering stay straight, but some/lots will cause the car to 'chase' undulations, make the steering heavier and the return to centre effect stronger. But as I mentioned, caster gives dynamic camber when the wheels are turned, when you need it. Wheels 'upright' when you need them to be, during acceleration and braking. Wheels camber when you need them to be, in the corners. Magic.
The geo print out on the first page says you have nearly +4 on the left and just over +2.5 on the right after setup but around +4 each side before. I would guess that's a mistake. Caster can't be adjusted on our cars during a geo session, it requires parts to be exchanged. I would suggest something is a miss with the geo sheets. If you have around +4 each side, you probably have LCA caster bushes or maybe/probably swapped top mounts. Look under the bonnet at the suspension top mounts, are the camber adjustment channels 9-3 on a clock face?
Bump steer, there are no positives.. it's always dogshit. Get it measured and more importantly get it dailed out. Our cars are notorious for it and getting nearly -3 camber on the rear from lowering alone suggests to me that it's lowered a long way passed it's comfortable working range. This will only add to the bump steer problem. You might even be getting positive camber on compression from the front arms. Bad times.
Do you have a more recent print out?
Also, anyone who says strings are useless doesn't know what they're talking about.