This is really neat - lots of nifty harmonic stuff (especially that crunch at measure 17 - I really liked that)! I haven't written much for voice myself, so I probably won't be terribly helpful but I'll toss in my two cents regardless.
The one thing I was really missing was some rhythmic contrast between the soprano and alto. I know you said that this is meant for amateur vocalists, but even some simple rhythmic contrast like a quarter against 2 eigths might be interesting.
Besides that I don't have much else to say - there are some small technical things in your score (text collisions and the like) that you might want to move around, but that's nothing major. Also, you might want to reformat some of your piano stuff into two voices rather than trying to tie them together as chords (ex. measures 21-24, piano left hand). But again, nothing major.
Nice piece!
