[Ramius]

Apart from recovering and recycling waste CO2, another angle to this process (if it is efficient enough) is that it could be another effective way to store and transport electric power. As methane, it transports nicely.

[Myrddin]

You figured out the value. If you have water, waste CO2 and the catalyst, you can transform back to methane (storable) with electrical input. Photo voltaic cells can capture solar energy and provide the input to do the conversion. Methane is much easier to store than hydrogen. In a closed system such as a space craft, that would be a useful way to manage the carbon cycle. It doesn't make much sense on earth. We can burn plentiful methane and let green plants do the carbon/nitrogen fixation for us using sunlight. My lawn is a spectacular tool for capturing CO2 all summer.