Should I write something to the reviewer who rejected my manuscript?
You really should respond to all reviewers in your response.  If the only comment was "the contribution isn't strong enough", then you need to reply showing why it is, in fact, strong enough.  You can say something like "We feel that this topic is relevant because x, y, and z, and this manuscript contributes a, b, and c to the field. We have reorganized the introduction to more clearly outline the need for this contribution, and have added a paragraph to the discussion demonstrating the importance of this work."

The second part is important because it shows that you're actually improving the manuscript in response to the reviewer's comments, not just blowing them off.