Now to an extent, that is certainly true. I wouldn't be very convinced of a religion if all the evidence it had going for it was the face of its prophet appearing on a potato chip. Even if that's a violation or suspension of the laws of nature, it hardly inspires awe. At a minimum, the miracle should be of such a scale so as to leave no room for doubt that it is a clear violation of the laws of nature.
At the same time though, is a display of power really the only criterion for judging whether a law-violating event is Divine? Let's think about it this way. If we expect the Creator and Lord of all living beings to give us a sign of His existence, how would it look? Clearly, it would have to be powerful, in that causing it would require bending of laws of nature. But I bet people will also have other expectations from this sign- it would have to be something beautiful, something deep, something truly meaningful, beneficial, and so on. So display of power is only one aspect of a good miracle, things like beauty, depth, meaning are also important. If God put up a lightshow in the desert sky as a sign, it would be awe-inspiring, sure, but I wonder how much depth and meaning it would possess.
There is something fascinating about the miracle of the Qur'an, in that it is God's revelation and miracle packed in one. Straight off the bat, we can sense that the miracle would be just as deep as the Divine message itself. The Qur'an is God's timeless counsel to all humanity, containing detailed spiritual, ethical, metaphysical, and legal knowledge that would be required for our life and optimal well-being. These Divine commands are expressed in a language that is not only beautiful and profound and subtle, but also law-defying and miraculous. So the miracle here mixes with the message- and at some points, it gets difficult to tell where one ends and the other begins. Is the revelation a receptacle for the miracle? Or is the miracle a receptacle for the revelation? That question is not easy to answer.
And yet, it goes deeper. According to theology, the word of the Qur'an is the very language of God. We often fail to realize how profound that is. As His final message, God- the Necessary, Ultimate reality of all else that exists- has chosen to speak in a human language, so we could hear and recite His own words verbatim. Every word of the Qur'an that we read is an expression of the intimate connection between the Creator and His creatures, every prayer of ours is, quite literally, a communion with God in the language of God. Mormon scholar Daniel Peterson in his article The Language of God: Understanding the Qur'an observes:
In Islam, by contrast, the "Word" is the Qur'an, the pure utterance of God himself, which human beings may themselves read and recite and of which, thereby, they may become co-articulators. Though few if any contemporary Muslims would agree to this, it is difficult to escape the sense that the reciter of the Qur'an, in a limited but important way, is unified with God in the utterance of God's own words. It is a kind of deification through speech.
I cannot conceive of a higher view of language.
Muslims, of course, would take exception to the sort of language the author uses, but the point about the intimacy between the reciter and the Creator is obvious. Perhaps another way of appreciating a miracle would be its effect on hearts and minds. Clearly, events happened in the history of time surrounding the Qur'an that are unparalleled in all of history. How it transformed and united the people of an entire peninsula, how it's memorized and recited by millions of people, how it has been preserved with no change for a millennium and a half- no book's impact was anywhere near that of the Qur'an. Perhaps these are not independent evidences of its Divinity, but these are things we would expect from a Divine miracle.
This is what is meant, I think, when it is said that the Qur'an is truly the strongest of all miracles. The strength of the miracle isn't to be gauged only by the number of laws it violates, and how spectacularly it does so, but also what that violation comes to signify. With the Qur'an where the message of God is the miracle, emanating directly in speech form from the Ultimate Reality, it is indeed the strongest expression of a Divine sign.
In this post, I haven't really been arguing for the fact that the Qur'an is miraculous, but rather for the proposition that assuming it is miraculous, it's exactly as we should expect from God. The other question of establishing the fact of Qur'anic miracles would require separate articles, essays, and/or tomes. On short notice though, here's an excerpt on the topic from a friend:
...virtually every ayah presents a linguistic problem (i.e. riddle). It seems like from the wording of the parts of an individual ayah to the structure of the surahs and then the Qur'an as a whole, every part of it is designed almost as if to provoke the question: why is it like this? Then when after due research and contemplation, the answer finally appears, it is like the key has been given to you to a door that had prior been locked. And every ayah is like this. And every surah. And the order of the surahs of the whole Qur'an. Then I felt like: what human being could have made something like this???