Lighter, slower, more visible, trained rider with some brain matter between their ears = safer. Speed kills. I don't really buy into the more power is safer thing, unless you ride on really really congested freeways where lane positioning is even more critical (if you ae a safety nut you shouldn't be there anyways) or you have some really sudden on ramps. Even a 250 has the juice to accelerate at average car speed.
Also, I was a skeptic, but ABS makes a big difference in preventing low/hi sides according to statistics. So that all kind of points to something like a higher end 650cc bike that has ABS (not sure if they make anything smaller with it) some bright headlights, and a tall stance (easier to be seen). Maybe a VStrom or 650GS?
'12 Sertao, '00 KDX220R '12 Tenere, '04 Tiger, '09 WRR, '06 DRZ, '06 TW, '01 250 EXC, '09 KLR