At 1x the dither looks fine, it only becomes noticeable and looks a bit out of place zoomed in. So, if your game's going to be displayed at 1x, then leave it, if it'll be zoomed in (2x and up), then consider replacing it.
While the newer walls definitely look better, I like how the old ones had a more lively silhouette for the tops of them. The new wall's simple smooth bricks look comparatively boring. I think the big bricks make more sense and give the walls more volume, but you could make variant tiles with the bricks shifted, chipped, etc if you want to recapture that liveliness.