I think that if you wanted to expand your services, looking into doing single killer shot sessions by request would be a good way to do that, especially if option B is your usual method. That way, people have a choice if they already have albums full of photos to document the costume, but they might still want to work with you. Though, I say to work to your own style, which goes for both cosplayers and photographers, so if that isn't your forte, people likely wouldn't seek you out for that anyway unless they already enjoy working with you otherwise and want to do something different.
I think that the majority of cosplayers, the majority of the time, would want option B, though, and might be like me and want option A only in certain circumstances. :]