@Joe Nation,
Infrablue and David are right.
As I wrote before, there are NO differences in how native Spanish speakers pronounce the vowels.
This doesn't mean there are no national or local inflections, slang or even grammatical tidbits.
A Spaniard would say "Buenass nochess".
A Mexican would say "Buens nochs"
A Cuban would say "Buena' noche'"
An Argentinian would say "Bueenah noocheh" (long "e", not "ee"; long "o", not "oo").
But they would ALL pronounce the U, the E, the A and the O exactly the same.