This plugin is needed when we have more pages to import than we can handle by hand, and that's exactly the scenario in which the layout is more likely to be changed. Then, the images need to be resized, and this is the perfect time to optimize the code to prepare it for a width change, since you are already iterating between the images and generating the code!
I've tried to find a workflow that would allow me to replace all the thumbnails with the right new size, no success, because although there are many plugins for that, none of them "predict" what height the new image will be and update the source code to match the name of the photo! All of them resize the image in the code, not modifying the filenames.
So, if your plugin (or any other) gets rid of the height in both the filename AND the code, anyone could search-replace the posts content to make them 240px instead of 300px, width, without worrying about height. Browsers can take care of that or another plugin that adds the proper width-height to the img code in pages.
If you add the resize option right in the options it would be MAGIC!