Sometimes when promoting our own particular views common sense observations are undervalued at the expense of our own bias. I like too thinking about this topic from a common sense perspective and then arranging my own particular view within that. First, it is quite obvious that the massive spikes of miracles in the Bible occurred at the foundation of the Old and New Covenants, making their authority attested. Under Moses many miracles were performed in killing being a representative of the law and condemnation under it. Under the foundation of the gospel by Christ and the Apostles many miracles were performed giving life, representation the salvation that the gospel provides and the deliverance from the condemnation of the law.
We see the order of things described here with regard to the new covenant:
We must pay the most careful attention, therefore, to what we have heard, so that we do not drift away. For since the message spoken through angels was binding, and every violation and disobedience received its just punishment, how shall we escape if we ignore so great a salvation? This salvation, which was first announced by the Lord, was confirmed to us by those who heard him. God also testified to it by signs, wonders and various miracles, and by gifts of the Holy Spirit distributed according to his will. (Hebrews 2:1-4, NIV)
Here we have the order. Salvation was first announced (i.e. the gospel), then God performed miracles to confirm and testify his approval of this new doctrine that was preached. More directly God's testimony did not only affirm the truth of what Christ and the Apostles preached, but was an unusual and heavenly vindication and seal of approval on their very persons and ministry as infallible guides on establishing the remaining canon of scriptures (so long as they remained teaching the same doctrines to the end). Once these scriptures were completed, they became the final authority in all matters of church practice and Christian living. Second, the only reason why we believe miracles to have occurred is because the scriptures say so.
Third, although Jesus is ‘the same, yesterday, today and forever’, we find God never continuously performed miracles anywhere in the Bible, but over long periods there was an absence of extraordinary physical miracles beyond that of prophecy. Even with the fulfilled prophecies many years pass at point in scripture where nothing new is fulfilled.
Fourth, as a matter of fact miracles do not cause people to believe in God permanently (eg. Pharaoh). They do allow for mammoth shifts in Salvation history, taking people 'by storm' as it were. They do overwhelm peoples minds to make them search for an explanation like concluded Jesus did what he did by the power of Satan, but they do not directly lead to faith, God’s word alone does that by his Spirit.
Fifth expecting miracles in order to have faith is in accordance with the Jews own wicked expectation of miraculous signs (Matth 16:4, 1 Cor 1:22) This may have partly been due to the history of miracles that God performed in establishing the Old Covenant as we have said.
Sixth, the parable of the rich man in hell talking to Abraham was one way in which Jesus tried to expose foolish human thinking that miracles were needed for faith:
“He said to him, ‘If they do not listen to Moses and the Prophets, they will not be convinced even if someone rises from the dead. ’” (Luke 16:31, NIV)
A wicked expectation/demand of miracles seems mostly due to a want of belief in the power of scripture and the Holy Spirit's ability to convict men of sin and bring them into salvation thereby.
Why do miracles 'confirm' God's word if they are not needed to arrive at faith? When considering how difficult it would be for a person without God's power to arrest the attention of a large body of people and introduce to them a whole new practice of worship and doctrine, we can see the miracles under Moses and Christ made this possible. Even Pharaoh had to stop and give attention to Moses and question his own beliefs and decisions. Also in the life of Christ, his popularity helped spread his fame. Miracles simply overwhelm human opposition so that even those who hate God and who would never believe, are yet arrested, even if for a moment to allow God's changing of the course of history and establishing of his kingdom as he sees fit.
Seventh, overwhelming miracles like under Moses or during the time of Christ were never meant to be God's regular mode of operation, otherwise they would be, for God is omnipotent and could do it as easily today and he once did before. To say that the people in those generations were more deserving of miracles due to their faith would be to conclude the most carnal opinion possible. These generations who were greatly favored by these miracles were also generations of the greatest wickedness. Those under Moses were destroyed in the desert as utter apostates and that generation under Christ killed the Holy One of God.
Note: In firmly arguing these common sense observations I am not implying that all external extraordinary miracles have forever ceased, only that if they did, it would not matter in terms of our faith and eternal salvation. I am also saying that it is not reasonable to demand them from those who we think have great faith or gifts of the Spirit, or claim to.