It's said about brain that, "use it or lose it" — now, question being, do you think if person plays brainless gambling games such as slots, dice for major part of his/her daily routine, will it make him/her dull?
Edit: "brainless" as in playing gambling games that does not require using brain, I thought it was clear especially given examples.
I don`t sure that "dull" is right word. Such gambler would become not interesting. And it even don`t depends on would his games be brainless or not. People must have different interests to be interest If someone will be in the gambling all day long - you would speak with him only about gambling. It is ok if you see him one time per month, but if he will tell you about gambling every day - you will be tired soon.