While VSTA has been pitched as a tool for the software architect discipline, I think of VSTA in a different way. I think of it simply as architecture tools. While useful for any of the various types of architects (http://blogs.msdn.com/smguest/archive/2005/12/12/503001.aspx) that might exist out there, the product's usefulness is not limited to those roles. The product is useful to anyone who works on the software architecture, whether they are an architect or not.
I also recognize that there are a large set of architects who are deeply engaged in the development process. These architects may find that VSTS's developer SKU also offers them significant value.