Despite concern over more than half of all Miami-Dade residential sales still being distressed properties, condos and single-family homes priced over $1 million are selling heavily thanks to attractive prices, low interest and an improving economy, realtors agree.    “We had a great January of pending sales in Miami-Dade and Broward,” said Ron Shuffield, Esslinger-Wooten-Maxwell Realtors president. “We wrote 48 contracts [of more than $1 million] between those two counties during the month of January, which is quite a few more than we’re accustomed to writing.”    Last year, the firm had 324 sales over $1 million, he said, up from 2010.    “Everyone has recognized that the values have probably seen their low point,” he said, “and they’re trying to make the best deals that they can before the values have a chance to start making their way back up again.”