Interesting -- so not only does mixing good news with bad like this anger the recipients and cast doubt on the leader, it doesn't even accomplish anything.
And thanks for reminding me that I need to read that book.
Machiavelli's point was if you have to infringe on your peoples rights, and do something negative --- then do them all at once. This way, time erodes the negative memories - and since they are all focused in point in time, then the series of positives that follow will move to the forefront of people's memories of your time 'ruling'.
Dan Ariely, from Predictably Irrational, has found that pain is best given in lots of small doses. People tend to remember the height of the pain, and not the time it lasted. Whether that result is transferable to emotional pain I don't know.