Cardiff Central is both the train station and the bus station, unsure of opening/closing times but along the side of the bus station there are establishments such as coffee vendors and Burger King.
BUT ... £5 for a single is extortionate, Mathers quotes £29 for a taxi, probably an airport taxi, yet the first of the goggle results "Cardiff Cabs" quotes £24 so with a bit of shopping around that fare could easily become less than £20 and if it's a family of 2, of 3, of 4 travelling then £5 per seat ultimately becomes more expensive than a taxi.
About the only thing wrong with the X91 service is the infrequency of services, once every 2 hours outside of morning and evening peak periods, I
used it regularly to/from Barry (Tesco's) and Cardiff and it was ever so quick a journey time and, I think, less than half the price of this new service. As for the other regular bus service, yes that is a pain and takes around an hour from Cardiff to the airport but then people will continue to use these "regular" services simply on cost alone.
Sure this new service is convenient for anyone arriving/departing Cardiff Central by train but other than that, taking in to consideration that people would need to pay for travel from/to their homes to connect with this service, and at the fare charged nobody's likely to use it for local travel (Cardiff to Barry as an example) I can foresee a LOT of empty buses darting around the Vale of Glamorgan.