I have a 2012 Street Triple R. I like the shorter reported seat hight and apparent better gas mileage of the 2013. Not currently a fan of the more angular design, but it would probably grow on me. Maybe you love it at first sight.
I however do not want a reported more "tame" gearing like on the 2013. I have never ridden a 2013, so this is just an assumption based on what I have read. Maybe I wouldn't notice. I am sure it is a great bike and down the line when it is time to replace the bike, if ever, I will buy a new one. Right now, in my current riding style, I want every ounce of hooligan I can get... it appears the 2012 gearing is a better fit.
Additonally accessories and aftermarket upgrades, if that is you thing, may be limited if there are enough changes on the 2013.
In the end though, buy what you want. It is your bike and whichever style fits your taste, go with that. I can't see how either is a bad buy. If you can sit on both that may sway you as well. Think it through though otherwise you may be asking again when the 2014s come out.
Just my opinion.