Yeah, it would be good. Maybe a drop down menu would be helpful with some common stock answers too to save you time. Maybe something like this could be implemented on the bad reports as well.
The addition of something like this to the report to moderator tool would be especially useful.
User: Report to moderator: [Spamming] <insert some extra information to justify choice> /send
Mod: *see's report*: <Agree>
<Disagree> <insert some extra information to justify decision> /confirm
In the case above the output is the offending post is deleted, a mail sent to the author of said post, the person(s) who reported receive a response according to the decision made. Those who were successful (according to their choice) get an agreed response, those who were unsuccessful get a disagreed response.
Obviously I haven't analyse the scenario completely i.e. investigated the extensibility of the feature above, but I think that the original suggestion made for the topic is very useful, it would be good to use that decision and relay it to the reporter(s) too.