Prices of Palm Beach single-family homes soared over the past year, headed by a blast of luxury sellers looking to unload properties ahead of changes to the federal tax code. Prices averaged $5.03 million in the 6 months ending in March, a 78% gain over the $2.83 million average in the same period a year ago, with private estates doubling from $5.52 million to $11.2 million. Prices increased due to estate sales during the year, which increased by 375%, as luxury homeowners looked to sell before the end of 2012, expecting a new capital-gains tax regime and a rise in taxes in 2013.