Reb wrote a long, articulate piece about submissions of poetry to magazines and prizes. Here's my comment:
I submitted a manuscript to contests regularly for five or six years. Got close a few times, but spent a lot of money and got no book out of it. (And postage for me is higher, from Switzerland.)
In 2006, I decided to stop submitting my manuscript for a year. I still haven't started again. Individual poems to journals, yes. Manuscript, no.
Because it was frustrating? No. Because it was expensive? No. Because it was boring. I simply got bored with the whole process. No feedback, no nothing. With individual poems, one does actually get some feedback -- acceptance, of course, but also (more often than guidelines imply) rejections with comments about which poems the editors were leaning towards.
With the manuscript-submission "system" that has evolved in the U.S. these days, it is almost impossible to get any feedback on a poetry manuscript. And after a while, that's just boring.