The single-family rental home market is booming, drawing more investors into the game. New landlords can update properties by year-end to get a special tax benefit, while others may want to do easy makeovers to help their properties stand out. "Rents are up, but the rental market is quite competitive," said Jim Randel, a Westport, Conn., landlord and author of "Confessions of a Real Estate Entrepreneur." He says tenants want "cosmetic comfort and