Inane means empty or meaningless. That’s all. A novel that is inane is boringly worthless; a speech that is inane says nothing in spite of all its words. Here is an example of Julie Andrews using the word correctly:
“The lyrics were a bit inane,” Andrews explained. “Actually what I did, because I couldn’t make sense of it and I have to have lyrics that make sense, I decided the best way to sing ‘I Have Confidence’ was to go completely nuts with panic and fear and busy work.”
She means that the lyrics were devoid of meaning, and that she had to find some way to invest them with meaning—an ironic meaning—before she could perform the song.
The fact that the word resembles insane (it’s only off by one letter!) seems to have infected the meaning of it for many writers. It seems to be veering toward meaning “madly stupid.”
Wrong: The goal is to gut derivatives regulation and the Volcker Rule. The reasoning is as short-sided as it is inane.
This was a subhead in Salon magazine, and the other glaring mistake in it (“short-sided” for “short-sighted”) shows us that this is a writer who is often led astray by similarities of sounds. Similarly, a rant by Allen B. West has this headline:
Wrong: The absolutely inane reason Cuba was taken off the terror list
And it begins with this sentence:
Let me clearly state that the pure definition of insanity is to continue to do the same thing and expect different results.
He could not make his own mental connection between the two terms clearer. Meanwhile, from further left on the political spectrum, a headline from the Washington Post:
Wrong: Inane attack: Jeb Bush not conservative?!
The question mark and exclamation point together tell us all we need to know about what the writer thinks inane means.
It is inconvenient that words sometimes change meaning, but it is after all a thing that happens to every language. The problem is that the people who know what inane means are pushing back. You will not find the meaning “madly stupid” even in Merriam-Webster, the temple of description-not-prescription, and you will find many columns by language nerds grumpily explaining that inane means empty or meaningless, nothing more.
For a large part of your readership, then, the meaning of inane has not changed. For a different large part of your readership, it has changed—or, rather, they never knew the correct meaning of it. No matter which meaning of inane you intend, many of your readers will misunderstand you. When a word is likely to be misinterpreted by a large number of your readers, you cannot use it to communicate effectively, and you have to abandon it.
Useful substitutes for inane: vapid, empty, pointless.
Useful substitutes for the changed meaning of inane: ludicrous, ridiculous.