Well, any good analyzer, like the one that's included in the Vienna Suite, will reliably show you a graphical representation of the frequency range. It shows what's happening in the audio. But it obviously won't start flashing and sound an alarm when a piece starts sounding "bad" ... π A plugin can only show you that there's so-and-so much loudness in this-and-that range, that's something that can be visualised of course. But a computer program can't "know" what sounds good or bad. That's something the artist has to judge.
It's not the response you'd want to hear, but what you're asking for is exactly how not to do it. π I mean, consider the humor of the statement: I don't want to rely on my ears. It's like a painter saying: I don't wanna rely on my eyes, or a cook stating that he'd rather not rely on his senses of smell and taste.
It gets better and makes more and more sense the more you read, research and practice. But if you think you can't, or don't want to do that, there really is no other option than to have someone else mix and master your music. A technical shortcut really doesn't exist, it can't.
And IMO, really just try to get better at mixing your own music. EQing stuff, making instruments sound good, setting levels, making instruments sit in the mix, not fighting or masking each other etc. I think you shouldn't really bother about the mastering thing. You can't really do it without a proper space, equipment and professional experience.
I can understand what you mean. Let me explain where I come from. As an artist, I am mostly a visual artist (I am an oil painter). That is why I compose visually -- I work directly on the midi editor, and I can't compose by playing instruments directly. As for mixing, this is why I love MIR PRO because it's a visual/natural way of thinking of my compositions and mixes. Honestly, I can't go back to the old way of mixing now -- it's very difficult.
On the other hand, one thing I do know accoustically is if something sounds good or bad, too loud or too soft, if there is too much low/high frequencies, etc. *But* my ears cannot pickup subtle things, such as, if there is resonance in this frequency range etc.. All I know is this sounds bad, which includes the piece I posted. So when I know this, I'd love a tool that will give me a visual feedback as to why it sounds bad...