macdo,
Regardless of high speed rail links, or similar, there is a mentality whereas passengers cannot imagine themselves crossing the border from England in to Wales to go on a holiday to, perhaps, Greece ... and I say this as an 'Englander' currently living just up the road from CWL
Furthermore it certainly isn't helped by the charges the 'Frogs' charge for crossing the Severn.
From CWL, as soon as one is nearing the Severn X'ing then it becomes a toss up between BRS and CWL, as soon as one is around Ross-On-Wye then a toss up between BHX, BRS and CWL, mid Wales then BHX, north Wales then BHX, LPL, MAN, so realistically CWL's catchment area is from Newport west across south Wales, not a vastly populated catchment area!
I was working at CWL as they negotiated the deal for the BA maintenance base to be built there, they were jumping up and down at attracting such business because there's, pretty much, naff all else business around to attract.