User acquisition and marketing company Fisku today reported a cost per loyal user decrease of 7 percent from $1.67 in its December 2012 Index to $1.56 in its January 2013 Index. The Boston-based company defines a loyal user as a person who will open an app at least three times. Compared to January 2012′s average cost of $1.14 per user, January 2013′s user acquisition cost is up 37 percent year-over-year, but the drop from December 2012 to January 2013 by 7 percent was not as dramatic as the drop from December 2011 to January 2012 by 59 percent, which fell from $1.81 to $1.14 per loyal user.

The company, which measures the average aggregate daily download volume of the top 200 free U.S. iPhone apps, saw mobile app downloads increase by 13 percent from 5.32 million daily downloads in December 2012 to 6.01 million downloads in January. With monetization company Flurry which saw 50 million iOS and Android device activations and 1.76 billion apps downloaded during Christmas week last year, Fiksu says the high trend of user activity and app discovery continued into January.

CEO Micah Adler says Fiksu’s January Indexes are early indicators of the “mainstreaming of mobile advertising,” meaning marketers emphasizing value over volume by spreading their budgets out for maximum profit, especially to mobile advertising campaigns.

“We expect brands to allocate more dedicated spending to mobile advertising campaigns in 2013 and to only get savvier about aligning seasonal spending to the ebbs and flows of user acquisition costs,” he says, in a statement.