believe it or not, amount of local radio play still is the most referenced metric for booking consideration, at least on a profitable touring scale (as in touring for income rather than promotion). downloads and internet fanbase metrics have been used as well for quite some time now, just on a smaller scale, ultimately these decisions are up to the promoter, whether to trust facebook likes to turn into ticket sales, whether to trust a new artist being represented by a historically successful agent (this probably holds more value than any online clout), whether to trust the promoter's own instinct with their local market in deciding what acts will prove successful. ultimately, i agree that making a back-catalog free will benefit certain artists but probably not the domestically touring indie band.