I agree with Lou, for the most part there is no particular difference in writing characteristics between a steel nib and a gold nib.
BUT, gold is a much nicer material, and many people who use, buy and collect fountain pens will view steel nibs as "cheap" nibs, and the gold ones as the "good" nibs. So if you want to sell to those people, you will need to be able to offer a gold nib before you break into selling pens for a "good" price!
So, is it worthwhile to put gold nibs on your pens? Yes! Particularly from the makers/sellers point of view. But this is very subjective, depending on factors such as the collectability of the pens. An example might be ashaw's president pens - I'm not sure if a gold nib would add much to those pens, since they are so special in their own right!
Just my opinion. [8D]
Scott.