The Mossad [Israel's spy agency] employs an estimated 2,000 agents and officers. The CIA is perhaps 10 times that size, and it's just one of 16 American intelligence agencies. Yet the quantity of resources has done little to improve the quality of U.S. intelligence.
Part of Mossad's edge is that it isn't trying to do everything. The only thing it cares about with respect to China, for example, is whether it is selling weapons to its neighbors. The only thing it cares about with respect to Indonesia is whether that country's Islamic terrorists are feeding into any networks connected to, or providing tactical tips to, its own terrorists. Russian nuclear ambitions are someone else's problem. And so on. One also suspects that much of the job of collecting non-Middle Eastern intelligence for Israel is placed upon diplomats using non-covert means. U.S. intelligence efforts, in contrast, lack that focus, especially since the Cold War has ended.
While the U.S. intelligence community employs lots of people (I've heard estimates of 100,000+ for all of the agencies combined) and spends tens of billions of dollars, much of that goes towards getting only a slight edge over commercial available sources with high tech and expensive methods like spy satellites and sophisticated maps of the sea floor in the East China sea, and low tech but cumbersome approaches like having someone assigned to read and digest every major newspaper in the world as a matter of course.
In contrast, one can be pretty sure that a much larger share of Mossad's resources go towards the function that only it can provide, covert human intelligence (i.e. spys). This is, in contrast, is only a small part of the U.S. intelligence machine, the smallest subagency within the CIA, which is only part of a multi-agency intelligence complex, and a small portion of Defence intelligence agency activities.