Like Robin mentioned in the post before this, Chennai just have to win a match or two to seal their spot in the semi-final.
Therefore, Dhoni should consider trying out some of the benchwarmers to get a better idea of the options he has before him in case one of the crucial players get injured.
I would prefer to have S.Vidyut in for M.Vijay today. Vijay has been doing well, but I'd like to see what Vidyut can offer on these South African pitches. He wasn't much of a success last year but, as you all would know, a year in the domestic circuit could have improved his skills. Moreover, his inclusion would give Dhoni a chance to try and break the record for most bowlers used in a T20 match! ;)
In addition, I'd like to see Ntini in the side for, perhaps, Albie Morkel. To be quite honest, ever since Raina, Badri, Dhoni and Haydos have been tearing apart all the attacks, I've felt that having an extra specialist bowler would help. When you have a batting order which is firing on all cylinders, it would be a good idea to have 5 bowlers (take Delhi as an example).
In addition to being an international veteran, Ntini offers some variety to the attack in that he bowls with a very unusual angle, which can really be useful when bowling across the left-handers.
However, Dhoni wouldn't want to disrupt the momentum and would, in all probabilities, go with the winning combination. Anyhowz, these are my opinions, and hope Dhoni would try them out!
BTW, it's nice to see the local boy, Bala, bowling yorkers at will! In my opinion, anyone who can bowl 2 or 3 consecutive yorkers definitely deservers a place in the national side. Pity, he wasn't selected for the T20 squad, but let's hope that he gets selected in future sides, perhaps at Dhoni's insistence! ;)