There was a lot of high hopes in Israel when he succeeded his father, that his rule would be pro-western.

For all of Franco's troubles, the conclusion was basically foregone when he appointed as heir a member of the royal family. Juan Carlos's father had long accepted an evolution into a constitutional monarchy should he ever regain the throne, as an inevitability; any smart person in JC's shoes would have seen the writing on the wall and would have acted in the same way, imho. I don't think it was luck, the forces in motion were already there; in a Cold War setting, a Franco-less Spain would have been subject to infighting between different franchist groups and would have suffered infiltration from Washington and Moscow, with the risk of a new civil war. A transition to a more legitimate government was the only way to reduce instability, it simply couldn't be done with Franco alive. South-American countries went through similar transitions at one point or the other.