We do not have access to the Goodidea theme for testing so our best guess is that the it also overrides the shortcode used to create the enhanced gallery and slideshow layout. When RPS Image Gallery is activated, it likely replaces the gallery feature set that is present within the Goodidea theme. So you are likely right to question the compatibility. You might consider checking with the theme author to see if they might have a solution.
Regarding the low quality images, you can update the thumbnail image dimensions in your media settings so that they are large enough or you can increase the number of columns in the gallery. There is an existing support topic that covers this issue fairly well.
Let us know if we can provide further support or assistance.