Hmmm... I agree that the change in swing weight will affect the performance of the bat itself. That's mostly down to user preference though, F=ma means that if he swings a 2.11 bat as quickly as a 2.8, then there will be an increase in performance. As to increasing the sweetspot size, most likely, again, to do with the swing weight etc.
If you're going merely by tapping a ball up and testing the 'ping', then I don't think the tungsten tape really makes a difference, but then again, I've never tried anything like this out.