Useless? By no means, automatically speaking.
But the pattern in Acts deals mostly with the miraculous happening before the sermon.
The
Acts 2 sermon is the result of the miraculous outpouring of the Holy Spirit.
Simon Peter's
Acts 3 and
Acts 4 sermon is the result of the lame man at the Gate being healed.
Stephen's
Acts 7 sermon is the result of the miracles he performed.
Philipp's success in Samaria was due to the miracles he performed.
Simon Peter's
Acts 10 is due to the miraculous visitation of an angel.
The rest of Acts continues in much the same fashion, wherever "street preaching" takes place.
The idea of going out to preach, and then maybe getting a chance to be used by God to perform a miracle isn't the ideal way.
At the end of Mark, we see that the Lord confirmed the word the Apostles were sharing with signs.
Preaching the Gospel without signs, wonders, and diverse miracles isn't going to convince a whole lot of people that what a person is preaching is of great value to them.