I've stopped doing dub plates (specials) for sound systems for well over 10 years. The principle behind my decision is that, for me, it detracts from the original song(s). I made that decision, sadly, after hearing a dub plate done for a famous sound by one of my favourite artists (also a good friend). Putting it mildly, I didn't think it did the artist any justice, nor did it do the sound system any favours.
Don't get me wrong; I've heard some brilliant dub plates in my time. In fact, I was privileged to be a selector on two sounds (Street Vibes from Brixton and Killawatt from Balham) and had happily 'voiced' artists for both. Back in those days, money was not an issue, in the sense that the artist did purely because he or she loved the vibe of the sound and the crew - not because they want to get paid. The pay was just a reward for giving some of the vibe back to the sound and its followers.
Nowadays, it seems as if the sound business is exactly (and only) that... business! You could, I suppose, argue that it's the way of the world. Yeah... I guess you could.
This, by the way, is not me being sanctimonious. I firmly believe in "to each their own". I would just merely suggest that if an artist is going to do a dub plate, treat it as if it was the real thing... cah yuh cyah fool di listener dem. Furthermore, I'm not one to ever say never (well, in this case, never again). But, as a matter of principle, I will continue to say no.