The main goal of trans-dimensional beings was to make our dimension habitual to them. But, it seemed like the goal was meaningless when they could always exist in our dimension without glitch.
When Enterprise was trying to destroy Sphere 41, they appeared on the ship to malfunction the Enterprise. Trip argued that their existence here was impossible. But, Phlox told that the space was altered (by increased spatial anomalies around sphere 41) enough that they could exist. This seems reasonable, but how did they appear in unaltered dimension at Xindi council?