Car jackings in Tanzania on the rise? Very interesting. Not sure where you're getting your stats from but from my time here this is the first I hear of this. Perhaps I must be a little more careful.
The place is safe. If you don't feel safe, get a dog. Everyone here is scared of dogs and stay away from certain beaches which have reputations for robberies. Besides that, for women, snatch and runs of purses is a common problem so I'd keep my purse close or just not bring it out at all...
I agree with the fellow above, 400$ a month in food expenditures is quite HIGH and you either have steaks every night or as he said, alcohol problems.