Revelation is not the most perspicuous book of the Bible.
John Gill has some interesting thoughts on it. He notes that it is false that "this silence the sum of this seal, or the only thing in it". Rather, it probably "includes the preparation of the seven angels to take their trumpets," in verse 2, "though none of them were sounded during this period." Also, some think it encompassing verse three, refering
to the time which elapsed, while the angel, who had incense given him to offer it with the prayers of saints, did so, and took fire off the altar with his censor, and cast it on the earth.
Others think it was a time of reflection or amazement, he notes. This also has merit; silence can be a profound experience, particularly in the presence of a King, of a great and holy one who is judging the earth in power. John's entire vision is only on the edge of the communicable; it may be that he was unable to express in human language the full meaning of this silence.
In terms of applying the book, some have interpreted this a period of peace in the church. But that gets into deep water where I don't want to go in one little post!
Whatever the precise meaning of the silence, it was certain a time of worship and awe. Sometimes we can benefit from the awesomeness of Scripture even without understanding the precise meaning, particularly in prophecy.
The opening of the seventh seal certainly was not impotent. Matthew Henry writes,
This was to introduce a new set of prophetical iconisms and events; there is a continued chain of providence, one part linked to another (where one ends another begins), and, though they may differ in nature and in time, they all make up one wise, well-connected, uniform design in the hand of God.
The reason that the seventh seal does not seem to have one main thing associated with it is that it introduced the next whole chain of events.