I've never ridden it as a whole route, just used small parts of it (such as the Coastal Path around Llanelli and wherever the path goes through Swansea), so please take my 'advice' with a big pinch of salt.
I'd suggest that there isn't going to be a great choice of wild camping sites because of the areas it goes through, which I'm guessing is going to be mainly farmland down in west Wales, or the busier parts of the coast?
I'd also be concerned if the highlight of the western part is the Llanelli Coastal Path. It's nice for a stroll with the family, but not worth travelling long distances for.
I'd also point out that the eastern side of the ride will mainly be going through the industrial and built up part of Wales, so there will be some lovely scenery (and some truly great MTBing), but perhaps not so great for wild camping again.
Very vague I know, but the info on the Sustrans site is deliberately vague to make people buy the map.