The new style panel should allow live editing of CSS rules. Since this is a key feature of the Inspector that we'd like feedback on, I'm nominating this for Firefox 4 betaN blocking status.
Are we writing a CSS editing tool or a debugging tool? If we're writing an editing tool then we should be doing this in a way that works OK with the users real CSS editor. Is this the correct trajectory for that? As a debugging tool, I think we're better off making sure we explain the misconceptions which lead to the fault brilliantly before we encourage the user to answer the problems by random selection.