That's easy: each other, and the intellectual fun that we all are out for.
Doctorow is clearly interested in having his work discussed from an economic point of view, so much that he will read with interest what I, an absolute nobody, have to say on the matter. The Econ-SF seminar should bring to bear considerably more intellectual firepower, and hopefully start to build connections between utopian SF and existing, or at least actually possible, economic institutions that might evolve into infrastructure for those economies. Remember, this is the narrative mechanism of SF anyway: I know that Anathem is much cleverer than your average SF novel, but that contains a proposal for the design of a learning institution that does not build Everything Killers. It's done by cleverly combining elements of modern universities (the Unarian maths), medieval universities and monastic orders. You can imagine SF being written doing similar work on development banks, or the complex schemes Ostrom found in the research leading to Governing the commons.
As for Mazzucato, or any economist... she gets to do what economics should be all about; blue sky speculation about how to pursue the common good, with new intellectual stimuli in the form of sets of assumptions that SF writers make for them. "Yes, but imagine we don't focus on incentivizing people to overcome each other, and try instead to create abundance so there is no need for rationing... how would it work then?".
The value of everything states clearly that societies need to decide what constitutes value. Except societies are not entities, they are emergent properties of the interactions across social agents. Economic institutions formed around specific groups of people with specific values and interests. Medieval banking families served the needs of merchants supplying high nobles with luxury goods found in distant lands, and, soon after, of kings in need of finance for their armies. The Washington consensus between the IMF, the World Bank and the US Treasury in the 1980s and 1990s represented the interest of international creditors, mostly Western banks holding bonds issued in developing countries. The infamous troika EC-IMF-BCE during the recent financial crisis represented the agenda of northern European countries. Can we imagine economic institutions that co-evolve with open source hackers and anarchists?
This should not be a hard sell. It's not for everyone, granted, but if someone does not get it, we'll move on to someone else.