I think it depends on the fair and 4H group- in my area we have actual drapes and curtains embroidered with the 4H group name and hung over each of the horses stalls and the tack stall. The only decoration we were allowed was a poster introducing our horse.
As long as the streamers are attached everywhere and not going to blow and spook any horses they would look good.
We are not human beings having a spiritual experience. We are spiritual beings having a human experience. -Pierre Teilhard de Chardin