I got so frustrated with the tire stores that I bought a used Coats 1001 computer balancer. It does a spin, dynamic balance. Static balance can be done on a bubble balancer, that's all. The Coats can do a static balance but I won't bother, only dynamic with weights inboard AND outboard. I always check static after dynamic because they interact.
Static balance prevents the wheel from hopping up and down, while dynamic keeps the wheel from wobbling. The wobbling is felt through modern suspensions.
Yes the idler arm can allow a shimmy condition, but most all vibrations are caused by poor wheel balance or a tire with excessive road force variation (stiff spot.) Loose suspension components will AMPLIFY vibration, but very rarely CAUSE the vibration.
If you were here, I would give you a 95% chance of my balancing those wheels correctly and making the vibration disappear.