The history of philosophy is that of geniuses getting so close . . . but missing the mark.
Hence, my appreciation of a thinker is often not “do I agree” but “can I learn” from encountering said thinker’s work.
It is not for nothing that I am apt to say appreciative things about Jeremy Bentham but not William Godwin. Is Godwin uninteresting? Never, on occasion, correct? Irrelevant. It is merely that making sense of Bentham and where he went both wrong and right is much more edifying.
Thus, often we must look for truth, but keep a special eye out for the interesting and profitable mistakes, even blunders.
The two most interesting failures in political philosophy, in the last two centuries? Herbert Spencer and John Rawls. I am not sure anyone else comes even close.
The errors of great men are venerable because they are more profitable than the truths of little men. — Friedrich Nietzsche
Wirkman Comment 
To the extent that I have looked directly at Bentham, it has been to try to locate clear statements of how he relates usefulness to psychological states. Thus, I am far from able to comment on him more generally, as I am highly distrustful of secondary literature.
However, I did read Rawls’ A Theory of Justice, and feel as if my only return on that investment was the ability to speak in an informed manner about a work popular amongst political philosophers.
I began to explain why I feel that way, but I’m not sure that it is appropriate for me to do so without waiting for you to explain more precisely what you to believe to be of value in Rawls; otherwise, I might inadvertently insinuate that you fail to see things that perhaps you see quite keenly. At the same time, I recognize that I am not entitled to a quick answer from you on that point.
I certainly do understand the idea of responding to this or that thinker as mistaken — perhaps ultimately quite mistaken — yet having made so close an approach to some previously seldom recognized or unrecognized important truth that his or her work should be still be valued.
I learned as much from Bentham’s lacanuae as from his forays into new territory. Others may not find him as useful. Rawls is so obviously providing a rationale for an unreasonable perspective that his massive failure can stand for the intellectual failure of the whole paradigm. I contrast Spencer and Rawls because they typify two contrary approaches: evolutionary and revolutionary justice.
Prior to AToJ, the political center-left seems not to have bothered itself about clearly identifying what they believed. He set-out to identify a coherent philosophical vision upon which most or all of the center-left could agree. His results were incoherent, and did not bring-about agreement.
But, while he was engaged in a philosophical effort whose failure is indeed interesting, I don’t see it as philosophically interesting. It is sociologically interesting. It is to be studied more as one would study a typical effort at religious reformation.
As far as that study goes, reading Rawls is intellectual time-on-the-cross. One would be no less improved as a social thinker if one could instead identify and employ a trust-worthy source to summarize the effort and note its deficiencies.
I must acknowledge that you didn’t claim that Rawls were interesting from the perspective of a philosopher as such.