Strangely, there've been very little kidnappings in Mali. It's only conjuncture, but it seems that AQIM prefers to kidnap in Niger. I spent over 6 months in Kidal, I've crossed the borders between Mali and Mauri multiple times, and never had a problem -- there's speculation about a mutual avoidance, i.e. the tribes, like Ifoghas in Kidal, don't bother AQIM so AQIM doesn't take action in their area...then again, there's not loads of foreigners around.
Bottom line, whether or not it's safe is not a question that can reasonably be answered. If you want 100% assurance you will not be kidnapped, you shouldn't go. Kidnapping is just a possible reality that we deal with in that part of the world.