Wonderful works were the least of Jesus, and His followers' job description.
Obedience to God's word is first and foremost. The disciples forbade an individual who was casting out demons in Jesus name. But the individual was not a follower of Jesus. Jesus doesn't even deal with the issue of the performing miracles in His name. Jesus brings up the fact if someone is doing a wonderous work in His name it hinders the individual from speaking evil against Jesus. The man or women would have no credibility to accuse Jesus of being false, if they are doing miracles in His name.
Mark 9:38-39
And John answered him, saying, Master, we saw one casting out devils in thy name, and he followeth not us: and we forbad him, because he followeth not us. But Jesus said, Forbid him not: for there is no man which shall do a miracle in my name, that can lightly speak evil of me.
Here is an example in
Matthew 12:24-27
But when the Pharisees heard it, they said, This fellow doth not cast out devils, but by Beelzebub the prince of the devils. And Jesus knew their thoughts, and said unto them, Every kingdom divided against itself is brought to desolation; and every city or house divided against itself shall not stand: And if Satan cast out Satan, he is divided against himself; how shall then his kingdom stand?
And if I by Beelzebub cast out devils, by whom do your children cast them out? therefore they shall be your judges.
Jesus tells the Pharisees that if He was using the name of a demon to cast out demons. Then what name was the Pharisees' children casting the demons out?
Miracles were not the indicator of obedience to God. The Egyptian magicians are proof of that.
Matthew 16:4
A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it, but the sign of the prophet Jonas. And he left them, and departed.
The power of the Gospel, the death, burial, and resurrection of Christ.
Jesus warned them against looking for the supernatural instead of the sign of Messiah.