Methinks some journalistic hype here, MV.
My (average saloon) car costs 15p per mile in petrol alone (total costs nearer 40p), and the current APD is £12.00. So the breakeven on fuel alone is 80 miles, i.e. 40 miles each way, with one person on board, twice that with 2 people and so on. And that's assuming APD is £12 at BRS and £0 at CWL (unlikely). The distance, according to Google maps from BRS to CWL by road is 63 miles.
I'm afraid that would not be enough to tempt me to Cardiff, all other things being equal.