What we see may mean something. And, more importantly, how we see things may mean something.
Does more importantly seem grammatically proper? Or, do you use more important?
I may not get what, more importantly, and, or, importantly may modify, here. I think an adverb, and, or, adverbial phrase modifies a verb, so, it may modify see? Or, may you use more important, and, or, important, as an adjectival phrase, to modify a sentence that comes after it?
If more important was an adjective phrase modifying the entire subsequent phrase how we see things may mean something then you'd need an additional verb otherwise the sentence would be incomplete. Because that phrase would then be a "noun", but there would be no outside verb.
So you'd need to do something like this.
[It's] More important that how we see things may mean something
Since this is not happening, more importantly needs to be an adverb modifying mean.
