According to Marc Cuban we are in the middle of his two-year-plan for a championship-contender - barring that Dirk doesn't fall from the cliff (there are unfortunately some signs that he's nearing it). Anyway: To contend Dallas needs more than one more (super-)star. The solution: Go for a restricted free agent before the trade deadline, who will have a big payday next season. The best available guys at the moment are Greg Monroe (4.1 Mio $), Gordon Hayward (3.5 Mio $) and maybe Evan Turner (6.7 Mio. $). I'm afraid they won't get Eric Bledsoe as much as I like him.
Why they should? Because only in that way Dallas can go over the cap next offseason. If the Mavs f.e. are able to trade for Greg Monroe (3-way-trade: Calderon and James to NY, Shumpert and Carter to Detroit, J.R. Smith and Monroe to Dallas) they can afford next year to go after guys like Lance Stephenson or Luol Deng and than give Monroe the extension. A line with Ellis, Stephenson, Marion, Dirk and Monroe looks pretty good to me.