If prophets were worth something anciently, they are indeed worth something today. God communicated to mankind through His chosen prophets throughout the Old Testament, and in Amos we read: "Surely the Lord GOD will do nothing, but he revealeth his secret unto his servants the prophets." There is nowhere in scripture where we are told that God would suddenly stop communicating with us the way He has since the beginning of time, and instead leave us with just a book to go on.
Ephesians 4:11-14 states:
And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers; For the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ: Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ: That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men, and cunning craftiness, whereby they lie in wait to deceive...
Unless I am mistaken, all other Christian denominations believe that prophets and apostles are no longer needed. They are described as the foundation upon which the Church was built (see Ephesians 2:20), with Jesus Christ himself being the chief cornerstone. Paul's statement (above) does not seem to be saying that while we need actual evangelists, pastors and teachers, only the recorded words of dead prophets and apostles are needed. We need living prophets and apostles, to whom Jesus Christ can speak. If the foundation upon which the Church was built is not continually maintained it will crumble, and the remainder of the structure will no longer be able to stand. Obviously, any church could decide to create an organization with individuals called prophets and apostles, and I'm sure that from the perspective of other Christians, that's all we've done. As I've explained, we don't see it that way. We believe that God is choosing the men He wants to serve in this capacity and that when they accept these callings and are ordained to hold them, they are not only functioning exactly as the Peter and the other apostles did when Jesus called and ordained them, but that they hold the same authority and power as did the original Twelve.