One museum reveled in its rebirth, another moved forward on its building project. For years, the Museum of Fine Arts has merely been talking about its massive expansion plan. This year, the work became tangible, as excavation began for the new American wing just as the MFA announced it was closing in on its $500 million fund-raising goal. Across town, on Fan Pier, the Institute of Contemporary Art attracted an unprecedented 300,000-plus people to its new space. Visitors filled the ICA's new galleries, theater, and wooden bleachers overlooking the South Boston waterfront.