It's widely known that Israel has nukes, and considering it's growing pariah status, a move like joining the NPT could only foster good will and perhaps give Israel a sheen of honesty over what is otherwise a greatly tarnished reputation among the majority of human beings. After all, it's readily apparent that Israel has only a token interest in real peace with the Occupied and it's neighbors, since low level warfare and tensions with it's neighbors necessitate American aid to be constant. A lasting peace would remove that need, and remove the artificially inflated budget that Israel now enjoys, and which the Settlers directly enjoy. It's American dollars that allow Settler largesse, after all.
27 injured in fire, explosion at former air raid shelter in Hamburg, Germany (DPA)
from the article: UN nuclear watchdog seeks to persuade Israel to join NPT