this question crossed my mind a few times,
i once had a terrible singer in my room, i tried a few different microphones and i never got a decent result (not even talking about Good);
in the end someone else sung that part of the song and it just sounded ALOT better ... even with a shitty mic i got better results...
its like my drumkit, sometimes my snare sounds so rotten, and i can't fix it in the mix or whatever, only because it sounded like crap when i played it...
but i think you won't replace the singer,
so playing with compression always is fun if the vocal track sounds bad anyway... don't let the singer stand too close to the mic,
you don't want too many plop sounds and sibilance,
don't record distorted, use compression to keep the volume up and the peaks down, and add a little bit of reverb to 'mask' the bad singing...
and and,,,, record your vocal track MORE than once, and play that together,
i sometimes had surprizing results when i did that,,,this seems to mask the "out of tune" notes a bit...and makes the vocal more full
and remember, if it sucks now, then it will probably sound nice in a year or so.... keep on practicing !
cheerz