I wouldnt play two spinners. All 3 seamers would play.What the joke? when the ball hasn't been swinging or seaming he hasn't done much in those 3 tests and a few first class games, so I would pick Martin and O'Brien over him on a lifeless track, thats what it boils down to. He will develop those skills in time. So I gather you will drop either O'Brien or Martin in the next test?... thats if they are going for 2 spinners.
For mine Southee's problem isn't that he is completely unthreatening when the ball is doing nothing, his problem is he doesnt have the match fitness to sustain good bowling over both innings of a test. This fitness only comes through playing more FC cricket, and getting more and more bowling into his legs.
We saw in England in the ODI's he was more than threatening when the ball wasnt swinging. His bounce and line is very good, and tricky if he gets it right. The more games he plays, the better he will get.
Anyway, I doubt Adelaide is going to spin a lot.