My camera comes with some software that needs the camera itself to be connected to run. This software far exceeds any of the native mac importers as I've found that they compress the files for some reason when importing them.
I have the same exact computer as you. Do not clutter the express card slot with an SD reader, you can get any number of usb powered readers for that, and most likely cheaper.
[off topic] Have you ever considered getting an SSD express card slot and installing your OS on it? I've done this and it has speeded up rebooting and app response time tremendously. It's like a whole new computer and our model is the last one to support express card slot in the 15" models.