Oh, why do I only see this thread today? In fact I finished my own Locke cosplay in August this year. And I didn't go for the exact Amano artwork either. I don't like some parts of it in case of one and entirely dislike the second.
So I started my hunt for fanarts with the nice help of some ppl writing frequently in the old school ff thread here.
In the end I based my own version partly of everything. I used elements out of the Amano artwork which I liked (like the zebra fabric and the gloves) but also stuck to the sprite regarding hair colour, the colour of his jacket and the colour of the bandanas and also decided on decorations like a necklace and wristbands just considering my this-is-locke-feeling. Plus I included stuff from some fanarts (and the PS) intro as already said.
It was really fun in the end
and although I don't consider my cosplay the best at all, I'm contend with what I did.
So I wouldn't say anything against a sprite based version at all. I think in fact its more true to the original than the artwork. Especially since many ppl who played the game don't know about the artwork.