You may be getting good coraline growth because you have low needs in the corals department. As you add more stuff and corals get bigger, they need more and more calcium. I would look at coraline growth more as a sign that you have good Ca levels and good Mg levels, now just keep them there and with proper lighting, you should have good growth from hard corals.
The benefit of the reactor is the ease of maintenance, set it, check once in a while, and you're good. With dosing, you'll need to adjust your dosing schedule/amounts as you add coral and as stuff grows.