There are two useful functions to refugia (well, more than that, but I'm simplifying for clarity).
One is nutrient export (growth of macro, removal of growth and therefore removal of nitrates). For this, a ball or an overgrown overflow isn't going to make a huge difference. It can't be a major plank in your tool box (mixing metaphors much...) in tackling the waste produced by the tank, though I wonder if it might make a marginal difference and that marginal difference might still be useful - even if it's only in the sense of, by taking up the small amount of excess nutrients it does, you're reducing the chances of a sudden growth in algae in the main tank.
The second is to act, literally, as a refuge. Particularly useful if you have fish or coral that like to consume plankton. Something like a ball-size or overflow filler can't be a main food source, however, and you won't be able to rely on it, but it will be a useful additional source of snacks.
Actually, Sea Turtle, one of the things that would worry me about your overflow fuge is that it's hard to maintain. Dying macro could leach nitrates and the living stuff could trap waste material in a way that also leaches nitrates (as opposed to just absorbing the nitrates). I say this as I did a similar thing with my previous tank and when I did actually clean it, there was a lot of crap down there.
You can see in this shot that the overflow was quite overgrown.
