Microstock Group - A meeting place for microstock photographers

wow, were you reading my mind? I'm also wondering about this. I just started to make some of my editorials exclusives. And over the month of June, I like to clean out those images that are selling with Dreamstime from other sites so I could make them exclusive images.
As for being Exclusive Contributor, I don't think I have enough in my port to make a diff, but it sure would make life easier not having to submit to non performing sites.

I do understand having some images exclusively for sale at DT. But I don't understand going completely exclusive with the #3 agency.

I haven't found DT to be particularly contributor friendly. Their sub sales are becoming a larger and larger portion of total sales. They continue to rule their forums with an iron fist, removing any thread without word or warning that contains even the slightest hint of competitors or expresses negativity. Their support often matches FT's and SXP's in effectiveness (and that is not a good thing). And, as has been reported here, they have become increasingly more picky on subject matter ("well-covered or too specific"), rejecting technically acceptable images that they think might not sell enough to pay for server space. As the only agency at which your AR plays into the search results rankings (that we know of, anyway), that pickiness can hurt you.

All you have to do is place a few images with them exclusively and you will know. Although doing this sort of research is important, nothing beats first hand experience. My experience , for the few images I placed exclusively, is inconclusive.

Yes, if DT favored exclusives like IS does I would consider it.  I'm really disillusioned right now with Fotolia rejects and SXP's prolonged death, SS has been consistent, but it is all old photos selling - nothing new.  DT has pretty much grown every month for me.

I have just a couple of exclusive images with DT, something I submitted to their "assignments". When I look at the total those images brought me over time, I must confess I do wonder if I should do more of those... it's especially nice now when images had quite a number of sales, since the price goes up considerably. Assignment files get 100 default downloads (at least they used to), so you images are ranked pretty high. I don't have any experience with non-assignment exclusive files though. Personally, I would never put all my eggs in one basket since I am making a living out of this, but if this a non-essential income, I don't see why not.

Since the change to their royalty structure DT has become a lot more attractive for exclusive photographers, before it seemed to make no sense to become exclusive on DT. But that change also scuppered my plans to upload a few test batches of exclusive images, they now only get a few extra percent royalty, still it might be interesting to see if those exclusive images come up in search more / sell better than the non-exclusive ones.

http://www.microstockinsider.com/news/dreamstime-royalty-change-makes-exclusivity-more-attractive

No. This is only for exclusives.