Just look at how much it has increased the last months. It is insane.
The price of $400-$450 does not really justify a difficulty this high.
If we stay around the $390-$420 for another month, then I can see another difficulty decrease coming.
Once people have invested in miners, they just have to evaluate the electricity cost vs the price of bitcoins they get.
They may not invest in new miners, but their existing miners will keep running.
Once the price increases (and people feel that it will remain that way), we may see some more investment in miners and then the difficulty will go up.