If I thought people in general were trying to gain-say anime-viewers in general (as one poster did), I'd resort to the geek heirarchy...but I don't think that's what we're really discussing here.
First: I don't discern any real influence of anime on D&D. Spiky armor existed before anime and will exist afterwards. Frank Frazetta was doing it in the 70s...and it was just as impractical THEN. Conflating some enthusiasts with the material, however, is rather ridiculous. As jcfiala points out, in the early 80s, we all wanted to be Jedi and Ninjas....and it was just as irritating then as someone wanting to be Drizzt a few years later or someone wanting to be Naruto after that (and people have been wanting to be Strider since the inception of the dang game).
Second: I like Naruto. I can understand why many would not. That's simply a matter of taste. However, anime (and manga even moreso) support a wide variety of types and styles, many of which never make it stateside. Compare Appleseed, Berserk, Crayon Shinchan, Naruto, Gantz and Sergeant Frog, just to use a simple example. Using Naruto or Dragonball as an example and claiming that all anime is just like it is pure hyperbole. Anime is broader than that. It would be no different than judging all detective fiction by Scooby Doo...or even all American animation.
Third, anime has many tropes...some are self-referential and some are cultural. Some are not. Many people don't need to understand those tropes to know they don't like them. When characters go 'kawaii' (i.e. cute-style) in an otherwise serious anime, some viewers are not going to like that. When an anime character spends a long time on a diatribe in the middle of a fight, some people aren't going to like that. Anime fans need to recognize that some of those tropes are things that non-anime fans really hate...non-anime fans need to recognize that many anime don't feature those tropes. You won't be seeing any cutesy moments with comic sledgehammers in Death Note, for example.
Fourth, Anime as we're using it here is an AMERICAN label. The Japanese would consider Batman:The Animated Series an anime, though we would not.
Fifth, anime is no more or less derivative than any other genre. Quick, how many films about turn-of-the-20th-century stage-magicians mystery-dramas were there last year? How many movies about invading aliens? How many police-forensic procedural show are on prime-time TV RIGHT NOW (I can think of at least six...expand that a little and I can think of more like ten)? How about medical dramas of e/r doctors at a hospital? Law and Order made whole seasons of 'shocking stories ripped from the headlines'. This is hardly an anime thing.
The fact of the matter is that anime covers a wide-ground, and some of it just isn't as popular here as it is there. Fantasy and SF-based material sells better here than, say, Sports Anime. Eyeshield 21 is hugely popular in Japan, but an anime series about a plucky group of wacky misfits trying to win an American Football tournament hasn't sold here (and Prince of Tennis was on CN's website for months before they decided to try it on TV). Mystery shows like Kindaichi Case Files (over 120 episodes) or Detective Academy Q or even Case Closed (Great Detective Conan) have no real following here.
It's also important to note that anime, in general IS targetted at a younger audience. This has been changing in recent years, but the target audience of some shows ranges from pre-teens up to college-age. Older protagonists ARE in short-supply...but that's by design and one of the tropes (just like it's a trope in fantasy fiction). Manga tends to skew for a much larger age range audience, so this applies much less to it.
In other words, it's a totally valid choice to dislike anime...but it helps if you don't paint it with a broad brush, no matter how much you do or don't like it.
