Angus, I've been using routers for many years and it's my main tool, however I cant think of any occasion where a laser light would have helped. what I do think is an important add-on for a plunge router is a LED light. Take a peek at this link to an old post of mine. Of course you're router may have a factory fitted light.
http://www.routerforums.com/53444-post34.html