The computers were strong enough to make visual tools possible even 20 years ago. It's the clumsiness and the limited expressiveness of interaction that limited the acceptance. I know: I was there. I remember reading Stroustrup who around the beginning of C++ wrote something like "we don't have to worry about ineffectiveness of headers in C++ because we'll anyway use visual tools soon." There were actually some tools. (http://en.wikipedia.org/wiki/Rational_Software "Rose 1.0 was introduced at OOPSLA in 1992") They stunk: http://c2.com/cgi/wiki?RationalRose
However, IDEs are alive and well, and browser DOM is stronger than ever - with "build your app" tools around each corner.
I doubted to put UML in there precisely because of Rational Rose and because UML didn't finally work as the basis for software architecture, but in the end that's still just a glorified C++ code generator - not an execution environment. Of course when your visual tool is a front-end on top of a traditional code it will have problems - you'll need a language that is designed from the ground up to work in a visual environment. And part of the reason why "visual environments" weren't created 20 years ago is because you couldn't execute the final program in visual form, in real time.
End-User development tools (rule-based like Agentsheet, graph-based like NoFlo or Blender graph editor, or even those based in traditional programming like Alice, Scratch or Code Combat) can be quite successful.
