As someone considering building a graphical builder of a kind you described - "dragging if statements and loop constructs out of a tool palette onto a blank canvas" - would you have any advice/suggestions on how to make it actually useful?

It's so true what you say about how this category of applications are often presented as revolutionary and prove to be limited, bloated, difficult to debug.. I'm thinking web page builders especially, but also various attempts at graphical programming. At the same time, there are in history some (more or less) successful examples, like HyperCard.