There really is only one way to find out.

I know this will make some people cross - but I wouldn't advise making any business decisions based on what anyone (myself included) says in a forum.....Unless you can establish a consensus backed up by hard data from a diverse range of contributors.

I fully agree with that. If someone is doing better than me at istock it can easily be that they are uploading much better and more modern pictures. I am mostly adding files of a similar style that is already in my portfolio there. If you have really good content you will outsell me easily at any agency. However I am still surprised that so many files are not doing better. And according to the stockperformer stats I am still in the top 50% on credit sales within that peer group, even though I am now indie, which is quite a surprise.

Just sold an image I uploaded last Monday so new images are still being found. I had a similar from the same shoot about 3 years ago so I think there are some good reasons to have a constant supply of images that you may think are too similar to other's in your portfolio, but the best match may never find.

OTOH, I've only sold three of the 100 I've UL'd since the beginning of January. A large portion of those were niche similar's so I will actually be surprised if I sell more than a handful of them (ever) but they weren't doing any good on my hard-drive.

And I've learned how to listen to nice music and enjoy a glass of wine while uploading so it's not a total waste of time.