I'd love to add him.
People are talking about adding a defensive big man instead, but there are two problems with that:
1) There are no defensive big men available that I'm aware of that I would have any interest in
2) We have about 45,000,000 bigs on this roster already, and can't play the ones we have
3) We are skating on thin ice in terms of backcourt depth - if any one of our rotation guards (Smart, IT, Bradley or Smart) gets hurt OR if either of our wings get hurt (Crowder, Turner) then we are going to run into some big trouble in terms of depth.
Likewise if we were to lose Bradley or Thomas we'd have zero outside shooting on the perimeter.
We really need an extra proven veteran wing / shooter and Martin could give us that, and there is no need to sign him past this season. He's the type of player who could have a real impact in the playoffs, and I prefer him over Joe Johnson.