Metro aggregation is one of the fastest growing segments in telecommunications in terms of data traffic. At the intersection of core and access, where coherent modules compete with direct detection technology, high capacity must be provided at low cost and low power, with enhanced scalability and flexibility. Real-life Telecom Italia Mobile metro aggregation networks are examined and their design and planning optimized. The analysis is supported by techno-economics, which compares two coherent solutions: traditional point-to-point (P2P) and digital subcarrier (DSC)-based coherent modules for P2P and point-to-multipoint transmission. We demonstrate that the greater flexibility of DSC-based coherent modules leads to significant cost savings over a three-phase network deployment.