Mandar,
Please be more specific by what you mean here when you say that high grade users means "High authority users". What specifically constitutes such a user? Is there a flag you have that denotes if the user is "high grade"? Are you referencing a custom or Out of box field that denotes they are "high authority"? And also, how exactly could these users be notified on a given case? You mentioned end users. Do you mean the affected end user on the ticket?
As I said earlier, the simplest way to control end user receipt of notifications is to establish the notification levels that the "high grade" users would receive. ie: users with a "high grade" would receive notifications only if they were to receive a High or Emergency notification and to do that, give those levels only the notification method associated. Their settings for Low or Normal Notifications would not even specify a notification method.
If that is not a viable approach, the only other thing I can think of is to include logic in the notifications to check the "level" of the recipients intended to receive the message. However, this would become cumbersome and tedious depending on the notifications and how detailed you want to get into controlling the notifications via conditional logic.