The recent integration of electric bikes into bikeshare systems has raised an important research and policy question: Do e-bikes merely substitute for classic bikes, or do they fundamentally expand the role of bikeshare? This study addresses this question through a longitudinal analysis of shared classic bike and e-bike trips in San Francisco (SF) and Washington, D.C. (DC) from 2021 to 2024. We examine the spatiotemporal patterns, trip characteristics, and network structure to assess how e bikes shape the bikeshare system over time. Across both cities, e bike expansion is associated with sustained ridership growth, indicating net demand generation rather than simple substitution. E-bike trips are consistently longer and faster, enabling bikeshare to serve time- and distance-sensitive travel and extending usage beyond urban cores. Spatial and network analyses further reveal a complementary relationship between classic bikes and e-bikes: while classic bikes largely support short, neighborhood-scale trips, e-bikes strengthen neighborhood connectivity by acting as mobility connectors for citywide movements. Moreover, differences between SF and DC highlight the role of urban context in shaping these dynamics: e-bikes rapidly become central to bikeshare usage in hilly, compact SF, whereas changes unfolded more gradually in flatter, more spatially extensive DC. Together, these findings suggest that rather than a direct substitute for classic bikes, e-bikes enhance the functional capacity of bikeshare systems, influence travel behavior, and reconfigure the spatial and structural roles of bikeshare within urban transportation networks. Importantly, integrating e-bikes can substantially enhance urban mobility and inter-neighborhood connectivity, offering a cost-effective alternative to building additional stations.