Just to give you an idea - Prior to Karma I was only up to 50k NS, had never raided, and was very limited in my growth. During Karma I dropped to about 20k NS and while I had a solid warchest afterwards, it wasn't that which put me up to 70k NS as much as it's been raiding. To have a 150+ efficiency after losing more than half your NS is thanks to raiding.
As for how the targets are, they are far slimmer the higher up you get, but I still find some here and there. Most of my targets are in unprotected micros - 5-15 man alliances typically.