I would take the Norn Crown off of the Prime and give him Regen instead. The Norn Crown would only make him an even bigger target. Then when you consider the fact that there is a psychic power that does the exact same thing it is a pretty big waste of points. TO save even more points you could take out the one Carnifex and add in another Harpy or Crone. I understand money is an issue in making an ideal list, but Carnifexs aren't that great of a unit.
The Deathleaper is a great unit, but taking Lictors with him would help. One big issue with the Tyranids are there great Elite choices, and only being able to take three of them. Armies are generally based around their troops, but Tyranids are based on their Elites.