Can adding many monobehaviour components to the game objects in the scene have a noticeable impact on performance?
For example, I will probably have 100 objects in the scene with a couple of mono behaviours attached (Most of which do not implement Update()). Should I be concerned about perfomance?
In my opinion, you shouldn’t really be concerned.
Check out the Optimizing Scripts guide.
It depends on how heavy your scripts actually are.
In any case, the best way to know what is the performance impact, is to make some profiling.
having 100 monobehaviours with no Update, is not slow. you shouldnt have a big fps hit from it