Bill Gates may have more money than he could ever spend, but there’s one thing he’s not willing to let go of: his sprawling Lake Washington estate, Xanadu 2.0. Despite being single and an empty-nester, the Microsoft co-founder, 69, has no plans to downsize from his massive 66,000-square-foot compound, which he originally purchased in 1988 for a mere $2 million. It’s now worth upwards of $130 million. “My house in Seattle, I admit, is gigantic,” Gates, who long held the title of the world’s richest person, told The UK Times. “My sisters have downsized. I can’t. I like the…..