Why would some images be saved to field_image / some maintain href after on import from Blogger?
The issue you described with some images not importing (keeping the blogger URL) is caused by the regex not identifying the image URLs as blogger hosted images. This regex can currently be found in the same file batch.nodes.inc on line 213 :

      if (preg_match_all('/(href|src)="(http:\/\/.*?\.blogspot\.com\/(.*?))"/', $node-&gt;body[LANGUAGE_NONE][0]['value'], $matches)
      || preg_match_all('/(href|src)="(http:\/\/.*?\.blogger\.com\/(.*?))"/', $node-&gt;body[LANGUAGE_NONE][0]['value'], $matches)) {


The code that worked for me is follows :

      if (preg_match_all('/(href|src)="(https?:\/\/[0-9a-z\.]+blogspot\.com\/(.*?))"/', $node-&gt;body[LANGUAGE_NONE][0]['value'], $matches)
      || preg_match_all('/(href|src)="(https?:\/\/[0-9a-z\.]+blogger\.com\/(.*?))"/', $node-&gt;body[LANGUAGE_NONE][0]['value'], $matches)) {


This could be improved but worked for me.  It allows for http and https.  And the .* was grabbing too much text before an image if there was a link above the image.

For the image quality, note that blogger uses different quality of image for displaying within the post and when clicking on the image.  Note the number contained within the URL s200 is low resolution, s1600 is high resolution.  Other numbers could be used for different size image.  You will have to decide which image to save or create a field to save two versions of each image.