Does it?
I have looked at the rail option for the Royal Welsh and it just doesn't work!
I'd be surprised if 100 people a day used it for the Show plus perhaps 300 on the special from Cardiff.
That's 1600 over the four days. The show attendance is c.220-240,000 each year. (So that's less than 1% by rail, if that)
400 daily means 10 extra road coaches - neither here nor there for the road network (there's usually 20 or more coaches each day anyway).
3 car trains full to bursting point apparently (I've not had the pleasure of working down there during that week yet).
Llandrindod is the focal point of that line. There aren't that many people from North of there going to Swansea or from the south going to Shrewsbury, but there are lots from both sides going to Landod.
Not that I support closure of any line really, but I've always wondered about the Blaenau Ffestiniog branch. Unlike the Heart of Wales, there is a relatively high quality bus substitute available along the entire route, and the line has regular serious problems with flooding. Since there isn't any nuclear freight down there anymore AFAIK you would think that if we had to close a line somewhere it would be that?