Google used a double sword language on this, because last year Cutts said that a sub-domain was considered like a new domain, then they changed their opinion and said that the sub-domain was the extention of the mothership domain.
So what I did a few years ago, was to integrated my contents on my e-commerce. It was also a marketing way to attract future customers and show any visitors that we were knowledgeable about our topic.
Now we have different article subjects and most of them are organized in different category of average of 25.
I am not sure how I can put an average of 25 articles per sub-domains or new domains, because after all, we will stay a small publisher compared to other sites.
My conclusion is that it isn't for us.
“Don't walk in front of me; I may not follow. Don't walk behind me; I may not lead. Just walk beside me and be my friend.”