Provided the current can reach both layers easily in their entry/exit points, additional vias spread through the track will not increase the current capacity. Instead, via holes will reduce the longitudinal cross-section of the tracks, reducing their capacity. Think of it this way: you want current to go through the X and Y axes, not Z.
However, if your entry/exit points are too narrow, some vias around them may help with carrying current to/from top and bottom layers.