Your solution for adding page/post interface to the widgetized areas is brilliant. The client uses the same familiar interface to edit the widgets.
The site I built uses the Responsive Theme by Themeid and the key to using images in the Responsive theme design is to use the "full-size" image 960x480 in the widget. In a full width browser where there are three widgets across the home page, the full-size image resizes to fit the widget width. When the browser resizes to under 600px wide the design adapts to a one column design and the image resizes to fit all the way across the one 600px column.
An error occurs when the image is linked to a page; the image no longer fits the widget, it extends beyond the the widget containing div.
Right now I am using a scaled down, smaller image in the linked widgets, but that breaks the design flow when the website is viewed on a smaller device. The normal solution is having the linked image fill the width of the smaller device (ie, tablet, smart phone) one column design.