Dirk Nowitzki isn’t exactly an eternal optimist. He deals in reality. So why is he smiling about the Mavericks’ chances in free agency this summer? Why does he think the Lakers’ Dwight Howard and/or the Clippers’ Chris Paul are realistic possibilities to join him in Dallas for his twilight years? There are many answers, but the most important one is money. The Mavericks have it this summer. They also will have a chunk of change next summer, too, he said Tuesday, when he acknowledged the inevitable truth that he will be facing a steep pay cut after his contract runs out following the 2013-14 season. That’s nothing new. He took less than a maximum contract in 2010, giving owner Mark Cuban close to a $20 million discount with a four-year, $80 million deal. Hall-of-fame caliber players typically sign for less money late in their careers. Jason Kidd went from $21 million to $8 million in 2010 and now makes $3 million with New York. But the point is that not only can the Mavericks offer a maximum contract this season, but they also could have enough to dangle another big (but not maximum) deal next summer.