I think one thing that would go a long way to moving thematic beyond the developer and courageous newbie crowd would be a central repository for function code snippets.
It seems that many of the things people want to accomplish require the development of functions that require a medium or better level of php programing ability. But many of those function have been developed by people and are just buried in the forums somewhere.
Maybe just a section of the forum where each thread was one tested function. The title describing what the function does and the text being the commented code. If there was enough material then separate sections in the forum could be set up for widgets dealing with the header, sidebar, body structure ect ..