If you want to keep the same level of economic activity, then low density requires a really good transportation system (be it more highways for private cars or better public transport). Roughly speaking, every person living in a city cluster should be able to reliably get to any other person living in the same cluster in 60-90 minutes tops, otherwise they are much less likely to interact with each other. More people inside this radius, more economic activity you will get (of course, it's not a linear dependency, the principle of diminishing returns applies here as well). High-density provides double win in this regard, not only you shrink distances, but also more people live inside the same area.

So until we get a transport revolution (be it autonomous cars, flying taxis, advanced concepts of public transportation or something else), I highly doubt low-density will be economically viable for core clusters.