The more, the merrier!
Spotters act as the eyes and ears for the costumers. Since vision (and hearing) is often limited, due to the helmets, or masks that we wear, it is vital (and necessary) to have spotters looking out for our best interests; whether that is pointing our potholes or poo droopings (at parades), or just letting us know that a little one is wanting shake our hands, spotters are absolutely essential.
Also, spotters are asked to ensure our safety by making sure that kids, or other event attendees aren't getting to rough with the costumers, a friendly "hey please take it easy with the trooper, thanks" works wonders.
Another side benefit to being a spotter is that you learn the ropes, so to speak. You learn how to gear up the armor and while you are at it, you learn a little bit of PR along the way. I am sure Mr Chilcote

can attest to all of this!
- Bill