How much time do you spend... fixing rejected images?
Do you fix each rejected image or do you move on? Would you have different versions then, each to liking of each agency? 

Also initially how much time do you devote to post production processing (excluding keywording?) ? 

I don't fix rejects... I move on with my life.

While its worth looking over rejection reasons, I don't think its worth obsessing over them - basically the effort involved with trying to re-work an image isn't worth the trouble. The danger with microstock is that it can be damaging to your self esteem if you focus on the rejections.

I think its worth getting your workflow to a point where you shouldn't be getting technical rejections (eg. trademarks, noise, artifacts) but if the rejections you're getting are "not suitable for stock" then sometimes it comes down to a difference of opinion that re-submitting just won't fix. Shooting something else is usually a much better option.

I only fix a reject if I am sure it is going to sell or if it is selling well on another site, most of the time I don't bother.  I try to spend less than 5 minutes on post processing but if it is something I think will sell well, I will spend more time and make sure it is how I want it.

I only 'fix' rejects for IS and only then if I think it has the potential to reasonably sell well __ it's unlikely to be worth the time to do it for any other site. Mostly the 'fix' consists of shrinking it down so it just qualifies for Large size.

Ditto - only for Istock and only downsizing.