I think we are applying the label ecological economics to two different things. If we think of ecological economics as a science, then we just fall back on the purpose of science - understanding the world. There are a pile of value-laden choices that anyone doing science makes, which loads the answers. However, the underlying purpose does not extend beyond understanding.
Disciplines are just groups of people seeking to understand the same small part of the world.
As a science, economics simply seeks to understand how humans decide to allocate scarce resources. There is no purpose here beyond understanding. Many people spend considerable time talking about the importance of a value shift to bring about sustainability. They also say that ecological economics must embody that value. Further, they also talk about the purpose of ecological economics being the discovery and implementation of sustainable ways of running the world.