The better dithers are fishes with different shapes/ swimming levels, IMO. I've seen a dozen plecos keep hidden in the same tank, until three silver dollar were added. Their movements, their flashy appereance and their appetites made the plecos stay out more and more time. Sometimes you could see all them out in the daytime. Among the best dithers are the barbs (most of them), pacus, bala sharks, opaline gouramis, most tetras and most rainbowfishes. Usually, bottom dwellers are NOT good dithers.
The "dither factor" is something you should really take in count when keeping more timid/ shy/ frightened fish. When a fish see other fishes in the open, it means there are no predators. If it looks around and is alone, or can see only fishes with its same habits, it can mean that there ARE preds, and it haven't seen yet. So it flees to hide. A dumb-type flashy fish like a bala shark or a pacu keeps moving all the time, and this tells the others that there's no danger and they can stay in the open.
Oh, almost forgot... A well-adapted dither, that is a good eater, can TEACH the mewbies what type of food they can find in your tank. And the dithers in "feeding frenzy" stimulate the newbies to eat the same food. So, the dithers 1- add movement to your tank, 2- make your fishes feel comfortable and stay in the open, 3- teach them what to eat and 4- stimulate their appetites. Sounds good, isn't it? Almost like magic, but it's NOT magic. Just a little trick...
Best regards.
Daniel.