I think it makes sense to establish a certain difference in style between the primary (left) and secondary (top) buttons. The primaries may be more 3Dish, with shades and highlights; the secondaries should be much simpler, with less colors, without any highlights or gradients. This contrast need not be too drastic, but may be very helpful.
From this viewpoint, the current node tool secondaries are OK, while for the selector, only the three last buttons (rotate and flip) are OK, others must be made much simpler, flatter and more laconic. The same goes for zoom secondaries which are currently "too beautiful".