These are good questions! I usually ask clients to mix down to 16/44 and 24/48 to get a good perspective of these issues as various people do it.
Lately I have been wondering if I should request 24/44 to have only to go to 16 bit rather than the 48 to 44 process as well.
Like ED said, I would also say to use 24 bit all the way thru to the end. You end up with a more sonically dense full 16 bit signal, and obvious better use of the A/D process.
And like Ed was getting at, if a 24 bit cd format comes out in 6 months, you are ready. I keep 24 bit copies of what I get/do for just these reasons.
Don't go back to analog, and then broadcast this because the broadcast compression process may bring out all the noise. It is not worth the effort.
Try to get it mastered as well to make the best of it.
Jim De Salvo
Audio Editing & Sonic Restoration http://beanstudio.homepage.com
"Nobody Hears It Better"