Well, I make my living from dj'ing at clubs, and producing music (releases on Yoshitoshi, Cafe Del Mar etc.)
I have a 13" 2008 alu macbook at 2,4 Ghz and 4 GB ram.
I use Traktor Pro, with timecode cd's or vinyls (CDJ 1000/Technichs 1210) with the Audio 8 soundcard from Native instruments.
After 1 1/2 year with my alu macbook, its time to part ways.
I initially bought it for its portability, wich i have been enjoying alot, and i havent had any problems with it.
Latency in Traktor have been an acceptable 2,5 ms, and i havent experienced any crashes.
I now have a 15" 2,4ghz i5, 500GB HD (7200 RPM) hi-res glossy on order.
The main reason for me to switch is the size of the screen. Its nice to be able to have a lot of playlists accesible in traktor. I went for the glossy display, due to the better viewing angles, wich is pretty important, as you dont allways know where there is space for you computer. I 'm ussually in a dark booth, so no problems with reflections (the lights are on the dancefloor).
On the production side its going to be nice with a bigger screen as well.
Eventhough i do most of my work on my 27" imac, i like to do some arranging on airplanes and trains, on my way to the next gig. For this the 13" has also proven to small.
To summarise: The 13" will do a fine job, but in the long run, you will become tired of the small screen.
Best Regards
Macchino
https://www.beatport.com/en-US/html/content/home/detail/1/beatport#app=a60a&a486-index=2