wooo hooo! As a Niners fan, I am absolutely pumped at this acquisition. Westbrook is nowhere near the elite back he used to be, but he can be an efficient backup/pass catching back. Alex Smith showed the most success last yr out of the spread/shotgun offense, and Gore is less effective without a true fullback on the field blocking for him. This will allow Westbrook to come in on certain downs to protect Smith, then set up a dump off if downfield is covered for Smith. It also pushes Dixon, who will still be used, to the #3 back and will allow him to learn behind Westbrook and Gore, and hopefully be ready to take the full-time backup snaps next yr. Also, allows M-rob to stay primarily on special teams, where is successful.
As far as the title/fantasy goes, no, this does not downgrade gore at all. Westbrook has had a solid career, but he is no longer elite and is highly injury prone. Gore is still a top 5 back and will get plenty of carries. If anything, this will help Gore stay fresh throughout the season and hopefully he will be healthy for all 16 games.