Monsters, Inc's re-release is definitely doing bad. It's 5-day (in mid-December) could barely match half of the Toy Story double feature from (October) 2009, which also had Cloudy With a Chance of Meatballs to contend with and was twice as long.
There isn't really a good way to spin that other than "well 3D conversions are not costly" which in all honesty doesn't take away from the fact that it is doing badly. To compare how badly it is doing, Wreck-It Ralph's PTA (for it's 8th weekend) is only 38% off of Monsters which likely has almost nothing but 3D showings, while Ralph is probably mostly 2D at this point.
That said the movie made truckloads back in 2001 so why bother saying how much of a failure it's re-release is?