A knight without a plume is just another soldier.
Except that nothing about a plume, or lackthereof, says anything about the rank of the warrior. Most historical knights didn't have plumes of any kind. Very few helmets in museums have the knot or ring required for attaching such things, at least.
Without a plume, the knight's helmets are like viking hats without horns: pointless and sad, with holes.
Totally different, though. The Viking helmet looks absurd without horns because the holes in it are gigantic. The holes in the knight's visor are tiny and barely noticable. And even if the regular plume styles came back, which you seem to be advocating, there would still be tiny holes in the sides of the visor. So either way, you won't be happy, according to your complaint.
I don't know why people think "kids these days" are so dumb
Are you presuming to say that if kids don't care about that particular detail, that they're dumb?
Kids may not have changed -that much- in 20 years, but they have changed. There's a lot more vying for their attention, and a lot of sensory overload. Flash-bang gets their attention more in this generation than small details. Consider, for instance, that modelling used to be a popular children's hobby. Now it's a niche hobby and video games are the mother of all entertainment. Small details don't have the same affect they used to. And further, I'm not convinced that plumes ever made -that- much of a difference. I'm sure, just like it would be today, some kids thought they were cool, and some kids lost them within 10 minutes of opening a set, or tossed them because they didn't care, or what-have-you.
When they see the plume-less helmets, they aren't going to get excited
I would say you're quite exactly wrong. Even -I- got excited seeing the visored helmet come back, and I couldn't care less about it's lack of plumage. Do you honestly believe most kids under 12 are going to look at the 'new' helmet (as to them it -would- be new) and say "It's really too bad that helmet doesn't have a plume, or else it would be very cool?" You're dreaming.
those pieces just aren't that cool on their own.
Entirely untrue. The helmets are cool in and of themselves. The plumes are a nice touch, but they don't make or break it. I have a small baggie of plumes that I haven't decided what to do with - and plenty of visored helmets and forestmen hats in use without plumes. They're cool without the plumes, regardless of whether or not you'd prefer the plumes be present.
If they do see plumes in these knew sets, I know they'll instantly realized that the dudes with the plumed helmets are a cut above the regular soldiers.
Why? I never saw it that way as a kid. All the forestmen came with plumes. Didn't make them -all- a cut above. When I was a kid, I saw the knight figures as a cut above the rest because they had the big, visored helmet and the big breastplate. The plume was a detail. A nice detail, but a detail nonetheless.
Take away all the little details and you have nothing left.
Except all the other awesome things about LEGO which made it one of the best toys in existance before plumes existed, and after they were largely abandoned. LEGO is loved by many for a lot more than plumes on one specific helmet.
So sure, I think it would be cool if plumes came back. That would be a great little touch. Do I think it's an absolute must? Not really. The new stuff is going to look great with or without them. And there's certainly plenty to keep me, and I believe virtually every kid out there, interested.
Forge not works of art but swords of death, for therein lies great art.
"The Gods made heavy metal and they saw that it was good." - Manowar