Let's talk some about it today,being exclusive on Dreamstime or another agency,is it really worth?
First of all I should say I haven't the experience to say yes or no,but have taken a look to some blogs lately and lots of people were on the same track.
What I learnt by reading those blogs is that it depends on you,your needs,what you expect from this world "the stock one".
If you're someone who just uploads few pictures in a month,then you should become exclusive with an agency,you'll be paid more for the few pictures you get to upload;but if you think to make this your own business or you can uplaod enough pictures in a month (around 100 or more) then it's not really the better way of going.
I say this because you have more opportunities by selling your pics to many different agencies,you get more visibility too and the sales will surely increase.
If you haven't taken a decision yet,then you should take a look at Yuri Arcus blog,the one I found the most interesting about microstock world:
After what I said,think about your needs before taking a decision or wait to see what fits you best.
Good sales to you all! :)