Is it worth submitting papers to "graduate" peer-reviewed journals? I am a first year PhD student in the social sciences at a Canadian institution, and I'm wondering whether it's worth submitting a paper to a "graduate" peer-reviewed journal. This would be my first experience in publication. 
There are a few different types of graduate journals. However, I'm referring here to those journals written and produced by PhD and post-doc students.
To my mind, the advantages would include: more chances of getting published, and this would be a great advantage in the first years of a PhD project; a smoother review process and, hence, more time to concentrate on courses and/or other projects. 
The quality of the work that these journals publish is very good. However, is it better, to wait, re-read and try to improve my paper in order to submit it to higher ranked journals?
You want to publish papers in the best journal or conference you can. If your Masters thesis can be published in a serious journal, you should attempt to send it there. Publications are the currency of academia and a publication in a better journal often translates to higher value.

However, there are lots of reasons to send it to a "graduate" or lower-tier journal. 


The journals in your field might consider a thesis to be previously published and they might not accept previously published work.
Your Masters work might be unrelated to your PhD work and you'd rather spend your time working on new more important work.
Your thesis would require a lot of work that would take away your new work. It might be better in the long run to work on new ideas as opposed to spending time trying to clean up or improve your previous work.


Without knowing your exact situation, it's hard for random strangers on the Internet to make an exact call. You should talk to your adviser or a professor in your department to get more informed and personalized advice.

EDIT: I should point out that my experience have all been in computer science. Things may differ in the social sciences.