AFAIK the only advantage to having a 64 bit machine is that you can address a larger section of memory as you can have 64 bit address rather than 32 bit address.
So if you are using blender for things that require large amount of memory, high polly work, sculpting etc. then the 64 bit might give you a bit of a boost (assuming the rest of your system is still pretty hefty). Otherwise I doubt you would notice any difference.