One difference between Wittgenstein and Mulhall is that Wittgenstein sometimes feared that all he was doing was destroying things, albeit houses of cards. Mulhall could surely never have that fear. Reading Russell Goodman's Wittgenstein and William James I was struck by this quotation from Wittgenstein on p. 63: "How needed is the work of philosophy is shown by James' psychology. Psychology, he says, is a science, but he discusses almost no scientific questions."
The work of Wittgensteinian philosophy, it seems to me, is essentially critical, even if also therapeutic. Goodman's careful reading of Wittgenstein and James shows how their work relates--where it differs, and how, and where it treads the same path. Wittgenstein clearly respected James, but wanted to point out where he went wrong (e.g. in thinking that he was doing science when he wasn't, or in thinking that something must be so when it need not be). This kind of work requires careful reading, but Wittgenstein focuses more on the attempted cure than on documenting the symptoms and defending his diagnosis. Perhaps because he is demonstrating his methods, or perhaps because he felt no need to defend himself.
In this sense some of Peter Hacker's work seems more Wittgensteinian than Mulhall's, at least in terms of what Hacker is trying to do (I haven't read this book, so can't say whether he succeeds). That's not to say that Mulhall is wrong to do what he does, but it is more positive than what Wittgenstein apparently had in mind. This still leaves me with the question of what to make of Wittgenstein's reading (if that's what it is) of Augustine, but I think that will require further investigation of the Investigations. There's also the question of what philosophers should do, but Goodman, Hacker, and Mulhall all provide reasonable models. There's no need for everyone to do the same thing.