At last, signs of a rebound. Despite sluggish Super Bowl ad sales, anyone with a television can tell you that there are many more new spots breaking - during event programming like the Golden Globes, the Bowl Championship Series and the NFL playoffs - than there were three months ago. Many of them were shot in December, when the Creativity Production Index - the average number of spots produced by a sample of agency offices - rose to its highest level since last March, following three months of steady decline. The Los Angeles Film Office likewise clocked December production day totals that were the highest since August, if still down 15 percent from the year before. Failures continue - Cylo got out of the spot business and Post Perfect was rolled up by its new owner - but it looks like the worst might be . . . Nah. We don't want to jinx it.