Okay, finally got a moment of downtime to answer this.

The first thing I'd do differently is to prioritise the development of economic diversity.

One of the most important aspects of cities is the way they create wealth, by facilitating the mutually beneficial exchange of goods and services. The possibility of mutually beneficial exchange depends on having a great diversity of actors doing a great diversity of things; if everybody is doing the same thing, there will be no differences that can be exploited for mutual benefit, and everybody will fundamentally be poor. Company towns based can sometimes appear superficially rich based on exports -- eg., everyone is a silver miner, which brings a lot of cash to town -- but this masks the fact that the city lacks an internal engine for wealth generation, and is thus fundamentally unsustainable.

(My foundation for thinking about urban economics, BTW is Jane Jacobs -- highly recommend "The Nature of Economies" for a quick primer on her philosophy.)

Arcosanti was developed in the absence of a robust economic theory -- in fact I'd say there was a general distain / distrust of economics, as was often found amongst countercultural 1960s types. Economics was regarded as an artificial human construct, the foundation of capitalist/consumerist greed, etc. In place of a meaningful economic theory, Arcosanti was initially developed on the basis of "sweat equity" -- you help volunteer to build it, and then you can live in what you built. But each unit of habitation takes roughly 3-5 person-years to construct, so to make sweat-equity work (in the absence of specialisation, finance, etc), you need to both be an expert in construction and be willing to live in a tent in the desert for 3-5 years.

That was the sort of vision that could inspire people in the early 1970s, but by the late 1970s had thoroughly burned itself out. So Arcosanti morphed into being a company town, whose primary exports were workshops, tours, and ceramic/bronze crafts. Not only does the company-town dynamic strangle actual wealth-generation, but this was a damn thin seam to be mining, and Arcosanti has been struggling to get into first gear ever since.

To avoid this, I'd engage in fairly conventional finance: take out loans, and offer properties for long-term-lease. Sell this to anybody who wanted to live there, whether they were explicitly in the arcology-building business or not. Re-invest the profits in more construction, and try to foster the generation of a complex urban economy full of independent actors from the earliest possible moment.

So that's the first, and most important, thing which I'd do differently.

The second thing I'd do differently -- although somewhat later in its development -- is that I'd try to focus less on design and more on planning. This is critical for the lessons of Arcosanti to be exportable elsewhere. You can't have a single architecture firm designing your whole city: just as you need to be able to accommodate a diversity of economic actors, you also need to be able to accommodate a diversity of infrastructural actors.

In other words, the question that needs to be answered is not "how should the arcology be designed?", but rather "what systems need to be in place to facilitate the emergence of an arcological design?".

Conventional urban planning is based on a 2D grid, with standards for property boundaries, zoning, design standards, interfaces to utility systems, mechanisms for resolving disputes between neighbours, etc. These are grounded in political, legal, and technological systems, which are loose enough to allow for a lot of creativity amongst architects, property developers, etc., but strict enough to ensure relatively harmonious interfaces between them. A physical megastructure -- the city itself -- ultimately emerges out of these systems, but the systems themselves are non-physical.

So, how do these systems need to be changed to facilitate arcological emergence? I don't have an a-priori answer to this: I think a lot of experimentation is needed. But that's where the emphasis needs to be.