I've got a very complicated GUI, so have a realtime GUI designer, that allows modification on the fly whilst running, and can generate code as required. This can then be passed back in for next time.
I only use Introjucer for quick/dirty layouts, and only use labels, e.g. for a form or document window.
Suits me, but I don't have a clue what I'm doing, so probably best to ignore me.
As hinted in other threads (http://www.juce.com/forum/topic/layout-class-gui-prototyping) I created a XML defined layout mechanism, you can check it out at: https://github.com/audiokinematics/juceLayouts
A debugger to display xml files as layout is also there, maybe I write an editor as well, but I would prefer being able to select and group components in the introjucer and write the xml from there...
Works for me, and if not contributions are welcome ;-)
I think you are only thinking about Rectangle<int>, where removeFromLeft(float) would be an overloading, but it would conflict with the regular removeFromLeft (ValueType) when you use Rectangle<float>