Below are upgrades followed by a comment explaining if the upgrade is essential or not worth the money.
UPGRADE - DESCRIPTION Health - The more health, the better chance of surviving. Streetsmarts - Prolong the victims breaking point (and by doing so, increasing your weekly income earnings). Remember to always try to buy them out first. Fighting - Increases your negotiation pressure by 10% for each upgrade. Speed - Not very essential. Only faster reloading is interesting here. Shooting - For better aiming speed and precision but not essential for taking over businesses.