I used to work in FC Parker, on the corner of Royal Arcade, and next to the old Spiller's records. Roger Harris owned and ran this shop together with Toytown (R + L Models in Albany Doad0. When I worked in Parker's we were essentially a toy and games shop, focussing on role playing and wargaming stock. This included Avalon Hill, Games Workshop, SPI and TSR games as well as citadel, Ral Partha, and Essex miniatures. The napoleonic display was to promote the Prince August range of moulds for casting your own miniatures.
Halcyon days, as you say John Hall tools had a modelling section upstairs, and they were in the adjacent arcade. Hywel williams had a toy shop stocking Hornby and Scalex, halfway down the Royal Arcade at the junction to Morgan Arcade. Beatties of London opened at kingsway, canton models was a short walk down Cowbridge road and Garth Models was not far from the flyover interchange at Western/Eastern Avenue, as well as the ones that have already been mentioned.
Cardiff was rich in Model shops and a real delight to make your way around. I also agree with all the coments about Terry's Trainshop in broadway.
Happy memories.