There are many other possible continuous node values, including probability of success of a given attack, likelihood that an attacker will try a given attack, and so on. In any real attack tree, nodes will have many different values corresponding to many different variables, both Boolean and continuous. Different node values can be combined to learn even more about a system's vulnerabilities . Every time you query the attack tree about a certain characteristic of attack, you learn more about the system's security. To make this work, you must marry attack trees with knowledge about attackers.
Different attackers have different levels of skill, access, risk aversion, money, and so on.
If you're worried about organized crime, you have to worry about expensive attacks and attackers who are willing to go to jail. If you are worried about terrorists, you also have to worry about attackers who are willing to die to achieve their goal. If you're worried about bored graduate students studying the security of your system, you usually don't have to worry about illegal attacks such as bribery and blackmail. The characteristics of your attacker determine which parts of the attack tree you have to worry about. This is because the cheapest attack requiring no special equipment is bribing the person who knows the combination.