The paper linked to by aet is quite interesting - it suggests that economists are mainly interested in the internal logical structure of their models and that these must be amenable to analytical solutions.

So perhaps the discrete diffusion simulation being discussed just doesn't look like what an economist regards as a "good" model.

[NB I've spent a lot of time writing simulations in the industrial domain - where the simulated result is generally primary and the logical structure is a means to that end].

I would say its as good an economic model as it would be an epidemiological model, if we changed 'wealth' to 'infection'.