Does MB D 12 actually make a difference?

Hi Friends

Iam confused about whether to buy the MB D12 battery grip or not.My main work area is advertising and people with camera mostly on a tripod.It would be helpful if you can guide me.I would like to know if the battery grip will increase auto focus accuracy/speed ?.Apart from the 6fps in DX which i will hardly use is there any thing else to justify the highly priced accessory?

thanks in advance

regards
Prasana
http://www.rprasanaphotography.com