Maybe we saw crazy hair once with the Kazon
But the Kazon were semi-regulars for the first few years.
Who was also a semi-regular. Horns were appearing almost every week in the Dominion War over on DS9.and horns once with Naomi
The same reason we saw few spotted races in DS9, really. Because Dax already had spots.
Not as many pics here as I'd have liked, but VOY did just as many weird noses and chins as foreheads...actually I don't really recall fins... instead of tons of bumpy foreheads and only one or two each of horns, crazy hair, etc., why not some bumpy foreheads, some horns, some gills, some crazy hairs, etc. Mix it up more.
http://www.bigmeathammer.com/Delta Quadrant Alien Database.htm
I understood your points and I agree.
