Balancing will reduce vibration at speeds over 28mph in my experience.

However, I build my own wheels to be true to + or - .005" total run out and use quality tires with reflective stripes so no heavy reflectors are used. Balance has not been an issue. I use Slime tubes f&r and on the rear a Mr. Tuffy tire liner. My top speed is 30mph.

Mounting the reflector about halfway between rim and hub makes a real improvement. Adding another oppisite also helps. Presta valve stems are lighter than Shrader type.