Second-home owners and property investors who can’t get homestead exemptions are seeing a big tax bite as primary residential owners lean on state tax breaks. The law requires appraisers to value all homes as of Jan. 1. For the most part, they compute values by analyzing sales of comparable properties over the prior 12 months. In 2007, home sales slowed considerably and, in many areas, happened only early in the year. Back then, prices had not yet begun to slip in some neighborhoods and condo buildings. That means higher tax assessments this year for about 80,000 homes among some 470,000 residential properties that did not qualify for homestead exemptions in Miami-Dade and Broward counties.