Chris.Ever get the feeling that you are talking to yourself Mick.
Zubrin has proposed using CO or CO2 NTR for a Mars RLV. Isp and T/W wouldn't be spectacular, but with the shallower gravity well of Mars and with plentiful local CO2 that wouldn't be a problem.
Solar dynamic is another possibility. A Mars generator would need bigger mirrors that the Earth version.
Mars atmosphere has .013% O2 and .08% CO.So is there an efficient scrubber for O2 and another for CO?If so separate the O2/CO out of the air.