Not really. Motifs are fine as they are. Especially since they are not superficial as you suggest. With the outfit system they have actual use.
Great to think of ideas, but we do not need to have everything in the game give a boost to something.
As for adding power, despite efforts made to balance, someone is going to show that some certain motif will have .01% more DPS. This will cause the player base to decide that every single other motif sucks and only one will be used.
If that were the case then we would not have 99% of the gear using one or two traits.