Most customers who aren't already into Final Fantasy aren't going to know about her existence prior to buying it. Most customers don't even spend a lot of time on online gaming sites. I don't think it's going to push any more copies than they will lose by people who dislike it.
People who are already into it but sit on the fence aren't going to be like "wow look at that rack that i might see like a few times over the course of 50 hours. Definitely getting it now, yup. Not even subconsciously. Half-dressed women isn't a scarce commodity on the internet. People aren't going to buy a 60 buck game for it.
for the record, sex doesn't sell all that much, at least not for advertisements
Sex catches attention, but that doesn't mean it sells.
