Yes, I believe it is true that plants which grow fast and/or have high lighting requirements also demand more co2. It also could be said that the more light you use, the more co2 you require.
In my (limited) experience the anubias is the most amazingly undemanding plant I've encountered. It is not particular about hardness, alkalinity, ph, temperature, lighting, substrate is optional and sometimes water is optional.

In some of my tanks I wouldn't even consider them slow growing.
The anubias barteri in my bluegill tank has grown quite large. This tank is unheated, unfertilized, has minimal lighting, and minimal co2. Yet it puts on at least a leaf or two a week. The tank does receive a 50% water change weekly (thank you python) so the minerals are there. However in this tank I use only tap water, and in this region it is extemely hard and alkaline with ridiculously high ph. So hard its not worth measuring with my test kit. I've not seen any other plant do so well in these conditions. But I'm sure there are others I have a java fern in this tank as well and its growing (
very slowly).
I put the internal filter in there for 2 reasons, as you guessed to increase mechanical filtration, but also for the circulation. The 2048 has a very powerful pump and the bluegill and his pet pleco (5 in.) make alot of waste.
