The Holy Spirit is important to effective ministry because it is the Holy Spirit who saves people. We get nowhere when the power is our own will-power. I have tried to convince others of the gospel, and have had NO reaction: positive or negative. I figure that was in my own power. I pray for God to speak through me, but am never great at knowing when it is Him and when it is me.
Miracles can validate a person is being from God. I do believe miracles can happen, but I also recognize that when the rich man (Luke 16) in Hades wanted to talk to his family (come back from the dead), he was told that if they didn't believe the Bible, they would not believe him either. And, we are told that faith comes by hearing(Romans 10:17) -- that we live by faith and not by sight (2 Corinthians 5:7) The Bible emphasizes Paul's words more than his miracles.
Having said that, I do believe that, I agree completely that the Holy Spirit includes miracles among spiritual gifts, for His own reasons, and that spiritual gifts are given to bring others to Christ for the glory of God. I'm not sure what would happen if there were more miracles.
I believe we don't see as many miracles because people lack faith that they can happen. If we have faith as a mustard seed, we can say to this mountain "move" and it will. One reason faith is lacking is that so many church father's over the ages have said that they are "no more" and so there is not much of a record on them. But, majority opinions, although they sway others, are not always correct. The Bible never says they are done away with. And, to me, Acts 2:16-19 indicates that they would be on the rise in the last days. Technically, the "last days" started with the Church, but I also believe that, as history closes out, there will be a resurgence of miracles. People are so lost now, and false doctrine is more prevalent than ever, that miracles would be a sign to show truth.