Since I had the same problem - which is the hard coded debug output at the wrong place - I wrote a small modification to fix this. After a while I ended up with a complete controller which can be downloaded at my website: http://johan.notitia.nl/downloads (check CakeBug Component).
It's very simple to use and very easy to modify (which I'm also doing :D)
You can always turn off debugging mode anyway.
This lead me here, http://bakery.cakephp.org/articles/view/debugging-with-firephp
Seems like a good thing to learn to work with. I'm always keen on any tools that can help me to produce better code.
Something already does exist that automatically reads the log (assuming its on in config.php) and sends it to Firebug every time you refresh. Sends other info too, like variables that you're passing to views, so you can see if they got set correctly. I haven't used it in a while, or with 1.2 yet though, so I don't know if it still works.
http://bakery.cakephp.org/articles/view/firecake-helper
You my friend are a genius.
I've actually been thinking about putting together a whole debug platform for CakePHP just like what you're thinking with the css hover, only I want to use some jquery/jquery-ui and make a couple of tabs for some of the variables like $params and $this->data, even possibly the controller dump when Configure::read('debug') > 2. I think people would use it. I haven't really had the time to research how to make it into a plugin you can easily add to your app and disable when in production mode. Anyways, this'll definitely work for now!