Most jobs require zero intellect. Just the ability to learn routines and follow orders. (think of how mindlessly gsm call center staff sound on the phone. As if they're robots).

What of bank jobs? Etc.
Jobs that dont require creativity ,logic or intellect.
Whatever smarts one needs can be picked up on the job. No need to stress ones self, besides if the organization is sizeable,inherent bereaucracy would frustrate any atmosphere for free flow of and implementation of ideas.

At the management level mediocres can still shine. And they do. Theyve been in the system long enough to know how to mechanically make decisions. Notice how the typical nigerian management is risk averse!
Yet they're probably got sheafs full of papers attesting to their smartness.

Every other thing is politics and bereaucracy.

So the question still remains , to be a successful employee ,is there any point in pushing yourself to be or appear smart?

#there some exceptions though.

Every company, institution or business organization is organized in a hierarchical system, and in order to climb up this hierarchical ladder, an employee needs to be smart, both in thinking, comportment and in his general approach to his job.

^^^
smartness at climbing the corporate ladder is usually machavelian smartness: politiking, conforming etc.
Comportment can be learned on the job.