It helps to have a standard of importance, in deciding whether Plato's Laws is important. Malcolm Schofield articulates such a standard at the very beginning of his Plato: Political Philosophy. Quoting Jeremy Waldron, he describes political philosophy as "a dialogue across the centuries". Thus: the Laws is important, if it contributes importantly to this dialogue. --That would be the case one would have to make, to show its importance.
Here is how Schofield develops this point in the very first paragraphs of his Introduction, which begins:
Is Plato our contemporary? Well, yes and no. When he philosophized about politics, he was thinking of the long-vanished Greek polis or 'city-state' of ancient Athens and Sparta.(Small Quibble Allowable in a Blog: I don't think I like that last sentence. Doesn't 'long-vanished' naturally fall within the scope of 'thinking', and thus what the sentence suggests is that these city-states were long vanished when Plato was thinking? Perhaps better: "When he philosophized about politics, he was thinking of the Greek polis or 'city-state' of ancient Athens and Sparta, now long-vanished." But to continue:)
Democracy for him meant the direct participation of all adult male citizens in the decision-making processes of the popular assembly and the courts of justice, not the representative systems of today.(True, but do those systems of today preserve the spirit and point of representation? Is the distinction between pure and representative democracy even understood today by most citizens? Thus it may not be entirely true to say that:)
The intensity of his obsession with political rhetoric as an inbred democratic disease is intelligible only against the background of an interpretation of fifth-century Athenian imperialism and its downfall in the Peloponnesian War that he probably borrowed (not without twists of his own) from the historian Thucydides.(But one might accept this as a concession that Plato's political theory is embedded in history, as Schofield next emphasizes:)
One particular event dominated Plato's conception of politics: the trial and execution of Socrates in 399 BC. So this book will begin by immersing the reader in the historical contexts of Plato's writing; and there will be recurrent re-immersions.(Then comes a very clever argument, ad homines and a fortiori, that we can't but regard Plato as a contemporary--which Dissoi Blogoi now "brings to you without commercial interruption":)
When Nietzsche spoke with enthusiasm of Plato's 'genuine, resolute, "honest" lie' (he had in mind the Nobel Lie of Book 3 of the Republic), however, he was thinking abouit general questions to do with morality, and more specifically of a contrast with the 'dishonest' lying--as he took it to be--of Christian morality. Similarly Hegel thought 'the Idea' of Plato's Republic contained 'as a universal principle a wrong against the person, inasmuch as the person is forbidden to own private property'. Hegel, of course, believed like Nietzsche that a philosophy such a Plato's could appear only at a particular moment in the historical process. Nonetheless in these remarks about lying and property Plato is treated not as a writer simply of a certain time and place, but someone still to be disputed with or invoked in aid. The assumption is obviously that at a certain level of generality there are themes and questions in moral and political philosophy, as in other areas of philosophy, which stay close enough to being the same over the centuries for a conversation of some sort between us and Plato to be possible and profitable.
That at any rate is an assumption I shall be making in this book.