The short version
The experience says players roll for rare pets. Decide how much cash you can spend while keeping a defense reserve, enter the live roll cost into the calculator, and stop at your planned roll count. Once you obtain a pet you care about, reassess protection before rolling again or leaving to raid.
Rare-pet hunting is tied to two risks at once: cash spent on the roll and exposure after the pet reaches your base. Because other players can destroy bases and steal pets, a lucky result is not the end of the decision. The next question is whether you can protect it without having exhausted your chosen reserve.