about the drip systems, I've used them for years, on all my tanks. I love them. I did have some with, and with out gravel, and still had same results. the difference between drip, and no drip is your putting water into the tank all day long at a constant rate, the fish feel like there in a big pond and will keep on growing. where as a closed system (NO drip) when you do your water change you do 10% - 20% I think it stress's the fish a little because of a fast change in the water perameters.
the thing about gravel or no gravel, you still have to do your regular tank maintance, without gravel, it seems to go alot faster. all I did was just siphon the poop off the bottom of the tank, and wipe down the glass. it goes fast, especially if you are running 20 tanks. Then just let the drip refil the tank. with gravel, I would siphon half the gravel every week, I would just loose too much water in those tanks, and I didn't want to fry any of the heaters on those tanks.
just make sure that you check your water before you put a drip on. make sure that there is no cholrine in the water, or you will have to put a carbon filter inline, before the drip. and another thing, if you live were it does get very cold with snow, you might have to but a bigger heater in the tank, or run 2 heaters. the water will get a little colder if you run a fast drip into the water.
I had about 180 3" discus in a 110 high tank, I fed them about 5 times a day, and never had any runts. the drip on the system was 5 gallons an hour, all the fish were healthy and just kept on growing. at 1 time I was changing things in my fish room, and I had to over stock a few of my tanks, and with the drip no problems. now if I had a closed system (no drip) I would've done water changes on that thing probably 2 times a day to keep my fish alive.