Spray bars or not makes no difference to CO2. The only time it makes a difference is if you run the bar above the water. You never want that kind of disturbance in a pressurized setup. What a lot of people do is set the spray bar up so that it runs parallel the surface of the water to lightly "boil" the surface for O2 exchange. Others will put the spraybar so the holes are pointing slightly down, or even have the bar vertical, so the surface is not disturbed, and do the surface movement with powerheads. What most people find in heavily planted tanks is that you almost always need a secondary source of water movement or you'll get a lot of dead spots. I even have a Koralia mini in my 20 gallon and that has a Fluval 204 on it.
I, as many beginners in planted tanks, overfiltered like crazy in the beginning. But I found that the extra filters are nice but not needed. It's cheaper, and easier to position powerheads to get the right flow patterns to distribute nutrients around the tank. A big filter is certainly nice to have a in planted tank, as the detritus buildup from the plant matter is pretty high, but a second filter is not a necessity, just a nice luxury, in my opinion.
I agree with has been said here. I run a 2073 on a very lightly planted 33G long and so far I find it works perfectly. For a 55G if it's more heavily planted, I would also recommend the 2075. These are really nice filters, btw. I'm delighted with mine.