I'm extremely doubtful that gas will go down much farther, especially into the spring/summer. First of all, if it gets anywhere near that people are just going to start using gas en masse just like in the old days. It's not like people saw the light when gas went up to $4, they just responded to the cost for a little while. If it stays down too long you'll start to see the hummers roll out again and demand will shoot back up.
Now, by next summer gas could still be down, like around $2.50 or so, but a trip for a family of 4 will still cost hundreds of dollars, so it's still extremely hard to budget for many.
Overall I just don't foresee a boom of people traveling just because gas prices are down. People are still hurting in the wallet and any unnecessary things like leisure trips are just out of the question for many. I do wish they would take the SB project off hold though - it's unseemly to have that gaping hole in the park this long, and as you said, it will aid attendance through and out of this thing. Don't look for that to happen though, there are more factors at play here than even what SDC decides. The ride itself is still caught up in European credit issues, right?