That is the question when it comes to Email Marketing. Perhaps more specifically, it should be “To add images or not to add images?”
Email clients these days often require a confirmation from the reader to download the images so using images in an email campaign or newsletter is not always a guarantee that the reader will see your pretty (and more time-consuming) communication.
I’d like to suggest that you do some testing to see which is more effective. Try and style HTML email but with no images (in other words, nice fonts, bold, rules, etc. but no images) with half of your list and a full-on image-heavy version with the other half and compare the results over a few email campaigns.