I like this (and not just because I am a fan of giant space hamsters, and even miniature giant space hamsters), but I think the focus is wrong. It is not the size of the economy that maters but rather the environmental footprint of that economy. Typically the size of an economy is positively correlated to its environmental footprint, but that relationship is not set in stone, and if we wish to avoid disaster (be it climate related or some other environmental catastrophe) we need to ensure that the environmental impact of our economy becomes truly sustainable in the not too distant future.
Otherwise we will be faced with one environmental problem after another, each increasing in severity and becoming more difficult to solve, eventually coming across one that we are unable or unwilling to solve, and we will all be much worse off because if it.
So we have two options, try to deal with each environmental problem as they crop up (and our experience with global warming is hardly encouraging), or work on a broader fix that addresses the root cause of environmental degradation. I think we need both.
Neither of these will be easy, but the only alternative I see is a planetary crash.
(h/t Michael Tobis)