There isn't a great way to do this, though I agree there should be. There are two mediocre ways to do this:
1) As you mentioned, there is a raise step. You can use it without causing the plan to fail:
<try>
<block>
<raise message="Hello, intrepid user, this is a message from the beyond"/>
</block>
<catch/>
</try>
This will cause a message to display in the plan run progress/history page. It will not cause the plan to fail. It will be highlighted in red as if it were an error.
2) Use a <sendCustomEvent> step:
<sendCustomEvent message="Hello, intrepid user, this is a message from the beyond"/>
This, in conjunction with the appropriate notification rule, will cause an email to be sent when the step is encountered. Post back if this method interests you and you need more information about how to set up notification rules.