I view the use of Modes as their own entity, or a way to emphasize between something that's not Diatonic with a certain Key. The more Diatonic a progression is, the less Modal sounding it is to me. Studying Modes in Diatonic Theory gives the reasoning behind where the Mode originated from, but doesn't necessarily give an understanding on how it's best used.
To me, Modes sound their best when used in non-diatonic function.
Example; If a progression went ....A---A---Am---Am---
I would use A Ionian over the Amaj and A Dorian over the Am Chords.
To really make an emphasis, I could use Amaj9 and Am7 chords. This is a Modal progression......