Well the truth of the matter is it matters but it hardly matters enough vs the perception.
SF isn't that hurt by a loss here, and if we lose (though it will stem the delusions about matching the 1972 Dolphins or 85 Bears) it just means we have to take one in SF.
Even so, home field is a much bigger deal for us than it is for them. SF has a home field advantage but it isn't as significant as ours, and it isn't the same kind of issue we might face playing a GB in GB. Playing in SF the travel and the weather are not as big an issue. Honestly if I could pick a place to play a road game, considering the impact of travel or the elements, if we cannot play at home SF would be a close second choice.
On the other hand, SF wants no part of playing us in the playoffs at home.
There are a lot of games in between that will affect the race, and a stumble here just means we have to focus more on one of the other games we might expect to win but potentially let slip. Those 10am games are going to be an issue, though the fact we have easier teams in our home schedule means it is likely we don't have letdown games against those teams because the crowd will not allow it.
The door won't be closed on either team, it is more of a bragging rights game than anything.
SF later in the year will be much more dangerous, with Crabtree back and a more experienced secondary. Then again, with Irvin, Clemons and Avril back as well as the additional threat of Harvin - we will be much more dangerous too. So it is the game in SF that will really be much more important on every level.
All this game is a chance to get a slight lead at the beginning of a long race.