I've read on other threads that the paintbrushes on TSI are replaced by CMs. My DS6 found one on our last trip sometime around 11:30, so I wouldn't suggest rushing by all the other rides just to get to TSI to find one the minute it opens--you may be able to find one later in the day.
My DS had a fantastic time making the plastic robots in one of the Innoventions buildings last fall. After listening to a brief lecture on plastics & recycling, everyone has a chance to participate in a computerized "build a robot & race them" game. After that everyone heads over to an area where they can actually put together their own robot--a nice FREE souvenir that the kids can play with the remainder of the trip.