The Cardiff Central - Bridgend Vale link should should be extended further west, to Swansea or even Carmarthen. Anyone coming from further west than Bridgend has to use 2 trains and 1 bus. 1 train, then onto the bus at Rhoose would be more appealing.
Also considering most of CWL's domestic/charter traffic during the winter departs before 7am. The first trains from both Cardiff and Bridgend dont arrive at CWL until 0623. Cutting it fine for any 7am departures and missing the morning KLM and some BMI departures before 0630. During the summer there will obviously be alot more daytime departures, but this will more likely be charter traffic.
Evening arrivals tend to get back between 2100-2300. The last direct bus/train link to Bridgend leaves CWL at 2051. The last link to Cardiff central is 2251, which you can then connect to the Central - Bridgend train. But is a very long way around!
The BRS flyer departs every 15 mins during the daytime, then every 30 mins after 1955-2255, with some early hours departures between 0230 - 0600 taking people direct to and from Bristol bus and train stations. Providing high speed rail links to/from the South West, South Wales and Midlands.
I think before worrying about battling with BRS and EXT to gain passengers from the South West, CWL needs to help out the passengers coming from West Wales whos nearest airport is CWL.