Just remember: As a rule, you know much much more about music then any singer ever will.
I knew that comment would raise a little uproar among the aspiring singers here!
I, too, feel the voice and singing are of upmost importance in a pianist's training. I was speaking from professional accompanist's viewpoint. Gerald Moore, the king of the accompanists who collaborated with all the greats (Schwarzkopf, fisher-dieskau, etc.) wrote a wonderful book entitled "Am I Too Loud?" It recounts his experiences in the world of accompanying. There are the art song singers and there are the opera singers. The former are usually much more musically complete in their preparation and they really do "collaborate" with their pianist. The pianist's role is much more important in song recitals and they will be the first to admit that their "accompanist" is much more than what that word literally means. All you have to do is try to play Schubert's Erl Konig to get the gist of what I'm talking about. On the other hand, we have the opera singers who only expect a supporting orchestral ACCOMPANIMENT who will follow their every whim during a concert. But the most that can be said about those concerts is that you only notice the pianist when things DON'T go well. A famous Italian pianist Giorgio Favaretto once accompanied Renata Tebaldi in a concert and his name wasn't even mentioned on the programme!!!!! I, myself, have learned a lot from many singers. ONe Russian tenor, Gregorian, taught me everything I know about the Rachmaninov songs. The concert we did together will remain as one of the most significant events in my life. I've also accompanied lots of bitchy divas and very idiotic tenors. Young singers who's only concern was their god-given voice. But I'll go along with them. They're the ones that are calling the punches and providing the food-ticket. But you can be sure that they listen to what I have to say and take my musical advice!
Sorry, that's the way it is. If you keep at it, you'll develop a good sight-reading ability and gradually learn the repertoire.