Rubbish, what are macs for if they are not for graphic design and photography?
Primarily looking trendy in front of your friends.
@OP:
More RAM will allow you to do larger edits without freezing up or crashing your editing program. But once you have enough RAM to do something complex (like spherical distortion or something) to a full size file without problems, you don't reallly need that much more. There would be an upper ceiling of usefulness at probably around 6-8GB for your photo editing purposes. Unless you do crazy things like stitching together 30-40 images in massive photomosaics or something.
CPU will make the edits go faster (but wouldn't stop you from freezing or crashing if you had insufficient RAM). Faster CPU = faster edits. Having multiple cores will only make some types of edits faster, and how useful it is for photo editing will depend on your version of software. PS CS6 is much better at taking advantage of multicores than CS5, for instance.
GPU (graphics card) will also be used by recent versions of photoshop to accelerate some types of edits.
There's no real way to just look at the numbers and say "that's enough." It depends on what you are having trouble with. Is your system just not able to finish an edit at all without hanging? More RAM. Is it just too slow for your tastes, but it does finish? More CPU + GPU. How much RAM is enough is when your system can finish everything it needs to do. How much CPU/GPU is enough is when it is fast enough to make you happy for how much you are willing to spend.
And SSD drives should not add any noticeable performance to photo editing. Once an image is loaded in photoshop or lightroom, etc., it is held in RAM and the RAM version is used for editing. it doesn't write to your disk and back constantly, so SSD vs. HDD doesn't matter except for the 1 or 2 seconds when you load or save the image.
SSD is more useful for other types of things that write to disk or read much more frequently. Like large database manipulation, or minecraft.