I've written up a rating system for use in an anime review show I'm hoping to do in the future, but I personally believe that it's kind of unbalanced, so I've come here looking for help with that.

My rating system works a lot like a school grading curve in that it measures each aspect of an anime and grades it accordingly.

My current system is as follows.

[*]Artwork (The least important part of an anime, but it's still a nice thing to have.) - Worth 10% of the final grade.
[*]Characters (In order for an anime to be good, you have to be able to like the characters.) - Worth 25% of the final grade.
[*]Voice-acting (Measures the quality of the voice-acting. For the sake of my review, this only refers to the original Japanese audio. The English dub will typically get a side review.) - Worth 15% of the final grade.
[*]Music (Music helps set the mood and is a necessary part of anime.) - Worth 15% of the final grade.
[*]Plot (Hands-down the most important part of an anime, without it, you don't have an anime.) - Worth 25% of the final grade.
[*]Personal enjoyment (Whether or not I as a viewer like this anime. Opinions vary from person to person.) - Worth 10% of the final grade.
[*]Gratuity (Generally refers to stupid or unnecessary fanservice. This is kind of a penalty score that subtracts points from the final grade.) - Worth -10% of the final grade.

I hope you can see why this needs to be balanced a little more. Just for the record, a score of 50% is average in this system and not 74% like in high school.

I'm looking for some constructive criticism and helpful advice.

What do you mean by stupid or unnecessary?
I like nude anime girls.

Plot is not necessarily the most important part of any text type. Take the classic film "Duel" for example, the WHOLE film centres around one central idea; the paranoia that a truck driver is out take out this guy while he's on the freeway. That is literally the whole film, which goes for a good hour and a half. Essentially there's not much plot and yet it's still a masterpiece.
What I'm saying is that plot isn't central to how good or bad something is, but how it is conveyed. I think it would be much more fair to set everything to the same weighting and just eliminate the "Gratuity" point altogether as that isn't something that is present in all animes.

To make the argument more anime-related and more contemporary. Take Redline for example. The story is basically cool guys racing in cool cars. That said the animation is top-notch and the music likewise. It is easily one of the best films in anime, probably even better than the Ghibli films that everyone and their mother has seen.

Also about gratuity, yeah no, this really doesn't work. Some people actually like the fanservice, no matter how stupid and unnecessary it seems. That or you have the wrong definition of fanservice and makes you seem as pretentious as the tone I have adopted whilst writing this post (that is to say, very).

tl;dr listen to CCS

When I say stupid or unnecessary, I mean stupid or unnecessary, and it isn't always restricted to that. Something such as the graphic rape scene in Kannazuki no Miko would automatically deduct the full ten points. What I mean by stupid or unnecessary fanservice is fanservice that is in no way relevant to what is happening, i.e.: when there's truly no reason for it (Like the fanservice in the Rosario + Vampire anime).

Plot, when you think about it, it's not so much the quality of the plot that is important as much as it is its mere presence. So only an anime like Ikkitōsen would score badly in this regard.

This post can be completely ignored, I'm half-asleep and some of it might not make sense. But you can read it anyway.
You missed something here. Bolded for you.
But a lot of the time, if an anime is ecchi, it always has the possibility of sex. Even if it isn't needed for plot, some people just watch animes just for fanservice. I myself have done this before.
Also, when you say 'truly no reason', do you mean the anime can do without it as well? Some animes make more sense on things via fanservice. Seikon no Qwaser is an excellent example of this. I couldn't completely understand the first episode as I watched it censored. Re-watching it uncensored made many things make a lot more sense.

I'm replying to the bolded; This refers directly to plot so your point is now invalid

That and fanservice doesn't mean just bouncing breasts and censored crotches. Continuity nods and shout outs are considered fanservice as well.

Are you guys going to help me instead of slamming me for disliking unnecessary fanservice? I came here looking for help balancing my grading system for an anime but if you guys are just going to tell me that my opinions are invalid then I'll just take my inquiry elsewhere.

That was not our, or at least my, intention. I just think that it doesn't deserve a whole field for itself. Can't you just lump it with enjoyment or something?

Or maybe just have a miscellaneous section.

explaining to you why your judgement criteria is bad counts as balance duder

better rating system:

robots?
yes > good stuff
no > trash it

Characters gay or lolis?
yes > trash it
no > good stuff

Character depth & development
yes > good stuff
no > trash it

Basically most anime sucks c***.

Yes. Yes. This. This is how you rate an anime.

Mechafags everywhere.