Money may not grow on trees, but dollar store sales are growing like bamboo. Which helps explain the recent bidding war for Family Dollar. A recent Reuters report attributes their vigor to the high volume of small purchases from low-income consumers. With increases expected in that demographic and an attraction to middle-class consumers for smaller shopping trips, the sector is projected to reach $57 billion in 2018. But it faces increasing competition from other mid-market discounters, the report notes.