I hope you noticed the difference between the way Kelsier got into the room and the way Vin did it. She walked up to the guards at the front and talked them away, rather than killing them. She just strolled through the guard chamber–the place where she killed her first time–instead of attacking. Why attack? She's powerful enough that she can just slip through and escape.
For Kelsier, the killing was always part of the victory. Vin's more goal-oriented, perhaps. In addition, she doesn't like to kill. So, her way is to just slip by the men. Then, in the room, she doesn't get close to the Inquisitors–she takes them down with tricks. On the streets, she would have had to use very little to gain much. She needed to be extremely clever with the small advantages she had. She used Allomancy in small ways to great advantage. Now that she's more powerful, I think her cleverness and resourcefulness will lead her to be far more amazing an Allomancer than Kelsier was.