I wouldn't wait for the MA en passant personally. I was going to wait before leaving my current Clinical Psychology PhD program to get an MA first, but a few people in the field gave me the advice that I would be repeating a lot of stuff, so it would be a waste of precious time and money (in my case as a second career student the time issue was a particularly salient point...). I made the decision around the end of this last October, with the counsel of those friends, that I would apply to a handful of programs as a practice run, which was quite comical considering I had to jam six applications, a general GRE (my other one was over five years old as of 2010), and subject GRE (I didn't need one previously) into the mix of my current doctoral work and family life (wife and kids) at dates that were very close to the application deadlines. So, I had much less preparation than I would have liked, considering it was a last minute decision. Yet, it turned out really well for me! I have now left my previous program and will be starting a new program this Fall with a solid APPIC APA match rate and an in-house clinic.
You already have a years worth of grades, and if they are stellar, 4.0 or higher, you would benefit from picking a handful of programs ASAP and applying this coming year. You are already well ahead of the game for next years application round. You could stay in your current program and apply while attending. If worse comes to worse and you don't get in anywhere this time around, you could stick it out for another year and get the MA en passant (if they will allow you to take it as a terminal degree) while applying again the following year. That was my reasoning at least when applying this year. If I didn't get into another program this round, I would have spent another year at my current program and applied again next round.
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Whether or not you will be happier, I don't know. I know that there are much better opportunities for me at my new program than at my previous program, so I'm extremely pleased. I don't think there is any way to be 100% happy with any decent program because at some point you will be pushed past your comfort levels in order to grow as a doctoral candidate. Figuring out whether that is what is happening at your current program, or whether it is truly a lack of quality in that program, is crucial.
In your SOP I would definitely approach the reasons for leaving your current program delicately but honestly. Likewise, in interviews, if you are going to cast a negative shadow on aspects of the program or your experiences thereof, I would try and balance it out by casting a positive light on other aspects of the program or your experiences thereof.