my excerpts lack the ‘more’ link

If you want to output the $post->post_content you need to use the_content() function, the_excerpt() function outputs $post->post_excerpt, so if the post doesn’t have content on the excerpt field it doesn’t output nothing.

A better solution should be a custom function that first checks for a user defined $post->post_excerpt and second for the $post->post_content and outputs the first defined.