Hi Morri2
The Mill is the Halifax Spinning Co near Goole (named after the Halifax bomber as it's on an old airfield) Google it then phone them as they never get round to seeing emails. However, I would have thought that the Natural Fibre Co would have more experience with something like Bowmont and would have the correct equipment to process it. If they were the ones to say spin it Worstead, then go for it. Woollen spinning would make the yarn fluffier and therefore 'softer', but worstead would make the yarn smoother and therefore with a softer drape. In other words it depends on what you mean by 'soft'
The thing is that you can't expect top quality yarn if the fleeces are not also top quality, but if the mill has seen a sample and they think they can produce what you want, then go with their advice.
Just being dusty shouldn't affect the quality, but if it has been stored wet or moths have got in then it is not worth using.
In my experience, selling all of a batch of yarn takes a long time, so your return may not be immediate and the whole thing will be a bit of a gamble. Hence your sussing out buyers with this question