You may have trouble getting that vibration out. As slender and long as they are, you probably would have to brace them 1/2 way between the current mount and the end to get rid of it. Not that improvements can't be made by making the center more rigid. It might help some to connect the two wings at the 1/2 pint. Maybe replace the aluminum plates at the end with abs to make them lighter?
I agree, I definitely wont get all the vibration out. But if I can reduce it by say half would be nice. When you watch black mounting arms, when hitting a bump, you can see them move a little and independently from each other. That little movement translated at the wingtips is large.
I think moving and/or adding a cross brace from the horizontal to vertical position might take some of that vibration/movement out.
Having 600lb front springs doesn't anything in this regard either at low speed.
CF endplates are in the future plans, which will help reduce the weight out at the ends. Looking to first play with the aluminum endplate shape and maybe addons to try and direct air out around the front of the tires.
I don't know, it's just fun researching, build and mess around with this stuff, then test it out and see what it does. Always been nerdy that way.