Some months ago, I reviewed a paper for a conference (with a joint submission to a journal). I rejected the paper with a list of points that were missing and suggestions for improving the manuscript.
Lately, I have been asked by the same journal to review a paper by the same group of authors. Note that this is not technically a re-submission, as the title is different. In the new paper (which is about the same topic as the previous one), the authors have added a substantial amount of new material and have taken into account some of my previous suggestions; yet, I believe that many of the main points I raised in the previous review are still valid.
Thus, I am tempted to repeat verbatim large parts of my previous observations. On the one hand, these are still valid, but on the other, I am not entirely comfortable with this form of self-plagiarism. It will be very obvious that I have simply reused my own previous work, also because the Associate Editor is still the same and because I have my own default format for reviews.
A related issue is that in this case the outcome could be different: given the quality of the material that has been added, I am tempted to ask for major revisions instead of voting to reject the paper.
What is the professional conduct in this case?