Chant is the only form that has official settings (namely, the Graduale Romanum).
Furthermore, chant has the important characteristic of being monophonic which brings forth the symbolism of the people singing una voce
, with one voice.
Polyphony, on the otherhand, has multiple parts and while it may be "more interesting" or even prettier, I'll admit...but that's not the point of sacred music which is to serve very specific liturgical ends. I'm lifted up spiritually most by the great negro spirituals, Gospel, and American folk hymns. That doesnt mean I think Mass is the place for them. Go to a choral concert if you want that other sort of stimulation.
Chant, for example, very clearly sings the liturgical text in a straightforward way with no repitition. With polyphony's multiple layers, however, the actual text can be hard to hear or discern the meaning of as they all sing over each other. In chant, the music serves the text...in polyphony (and all later decadent forms), it seems the text is made simply a vehicle for the music and showing off the talents of the composer.
I'd be careful of saying polyphony lifts you up more spiritually, as chant by definition is designed to be the most spiritually beneficial. Spirituality is not emotions, in fact it is quite the opposite. Polyphony gives me a good peaceful/transcendent feeling,
a "beauty ecstasy" or "church high" too...but that's not what spirituality is about, in fact that's base sentimentalism.
Actually, I wish more Masses were symphonic, like Mozart's Requiem.
"Dressed up" Masses strike me as sort of like what the psalms and Jesus talk about when critiquing Jewish Temple sacrifice. God doesnt want our bulls and cows. And he doesnt care for all our gold and violins and dress-suits. He wants our souls. Giving him "our best" has NOTHING to do with expensive or complicated externals. Worship that should be done in an ascetic way, in monastic fashion, not in one that immerses us in sensory enjoyment. All this striving to impress God (and too often other people) with these efforts at greatness, of ostentatious churches and art and music...is still so much dust. Great human talent has its place, but it is no more objectively "better" in worship than anything else, no less vain in God's sight. He's not impressed, and neither am I.