Generally, I'd say they wouldn't sign a player like Martin, since he actually has legit SF size. But in his specific case, I wouldn't be surprised. In addition to legit SF size, Martin is a solid three-point shooter and after spending a few months with the Hawks, has to have at least an elementary understanding of the Spurs' system. He's a sub par defender, but Jeffers isn't big or strong enough to defend SF's at this level anyway, so who cares.
As far as trades, it's the same old story. They're too arrogant, stubborn, cautious, clueless and reactive to make a potential game changing trade for a player the caliber of Young or Green, who's a lesser version. The absolute best I could envision them doing, is either Bonner, De Colo and a 2nd (or overseas rights to anyone but Bertans or Jean-Charles) for Marvin Williams or Bonner and either Ayres or De Colo for Bass. Most likely though, they stand pat on that front and sign a washed up scrub such as Howard or Pietrus for the remainder of the season after they fail to get what they want in the buyout market.