I've bought a few power tools over the years, used them once and regretted buying them, but I love my old Black & Decker router!
Over the years I've made loads of hardboard templates for routing pickup cavities, battery compartments, jack sockets etc. I even used the router to reshape the cutaways of an old Fender Bronco body, a bit like your Musicmaster. Never had an outright disaster with it (touch wood!)
I'd be much more nervous about attempting, say, a fret job than routing big holes in a body!