With regard to vowel-centric versus consonant-centric languages, English tends to be consonant-centric, and that's partly why our spelling is difficult. For example, "flutter" could be spelled "fluttr": we don't need the 2nd vowel and thus wouldn't have to guess whether it's spelled "fluttur", "fluttor", etc. English could use a refactoring. Examples: http://wiki.c2.com/?RefactorEnglish
What you're referring to is essentially schwa-reduction. Unstressed vowels in English get reduced to a neutral vowel sound (represented by schwa, an upside-down e), and different letters are used to represent that vowel depending more or less on linguistic history.
But vowels do matter in English. Consider the following words that differ only in the vowel they use: bat, bait, bit, bot, bite, boat, boot, butt, bet, beat, bout. Furthermore, all of those words refer to very different things. Semitic languages are based on a triconsonantal scheme, where three consonants define a root, and the choice of vowels implies inflection. Dropping the vowels in Semitic languages does not impair meaning all that much.
I didn't intend to imply all vowels can be dropped or wild-carded in English. As far as schwa, if we do refactor English, we should probably stick to existing "normal" letters rather than introduce symbols such as an explicit schwa. I agree this risks either ambiguity, or some potentially non-obvious rules to remember.
As it is, I feel sorry for non-native English learners; English's spelling is a mess. The only saving grace is that being semi-phonetic means one can often make a decent guess.
