Having a star performer employee is great. Having two or more is fantastic!
What you need to watch out for though is sometime's the knowledge of the business can be held by only one or two people.
So what happen's when those people go or holiday? Does the business come to a standstill?
Be careful not to let too much knowledge be stored up in particular invdividuals. rather work as much as you can to ensure the knowledge is spread around.
Just in case.