Often that seems to happen, usually with the comment  over-filtered/over-processed , (I think this relates to me tweaking white balance and brightness)  anyway I never bother resubmitting  - should I or should I not?  Does anyone resubmit?

Thanks I think I will with some, as they are good sellers elsewhere

I usually don't. For one thing, I used to find that I would just get another rejection reason after wasting time trying to sort the first one out. For another, it involves reworking a file just to submit to one agency, while with the same amount of effort I could prepare a new file of something else to submit to all of them.

I resubmit if I think I can fix the problem easily and if I think the image will get some sales.

Of all the agencies I've found the iS inspectors the most helpful in learning how to fix problems.  Some of their rejections - particularly the dreaded "Artifacting" - can be difficult to figure out the problem.  Sometimes an inspector has included an enclosure containing the part of the image with the problem.  Usually it has been some small CA or posterization that was not noticed by me or inspectors at other agencies.  Sometimes it was not visible (to me) at 100%, but was clearly there at 200%.  These enclosures have been very helpful and I've only received that kind of personal attention from inspectors at iS.  Now that I know what to look for I can find and eliminate those problems before submission, which has improved the quality of my images at all agencies.

By fixing and resubmitting you will get a better idea of what they are objecting to and can then correct those before submission.  In my experience, "over-filtering" can often be fixed by lowering the saturation a little.  Of course, for other agencies the "over-filtered" look may be more desirable and sell more so it's a balancing act.  If you feel you're still learning and want to figure out the reasons for the rejections then I'd recommend resubmitting - for me this has been a great help in improving my photography.  Of course they still might get rejected for other reasons as pointed out by BT, but at least you can have fixed one issue and will learn something in the process.

It is situational for me.  If the fix is easy and I just missed something, I will tweak and resubmit.  If I know they are wrong, I resubmit, but not as a resubmit...as a new upload.  Or I go to Scout who provides enlightening insight.  "Please edit your image while at 200% or 300%".  Seriously? When they "claim" their inspection process is only at 100%.  I will go on record here that in some cases they inspect at greater than 100%.  I have a diamond friend who gave up on them for this exact reason.  You can find a lot of flaws if you zoom in to those levels.