Anyone here w/ experience upgrading MBPros think its worthwhile to upgrade the original unibody machine at this point? Its currently got 4GB Ram, the 2 GPUs, 2.53 GHz Core2Duo, 320 GB HD @7200. I actually like the fact its got FireWire and not Thunderbolt as I've got plenty of FW drives, audio interface etc. So are there any options to upgrade this thing that make sense? Its still a good machine as is, its really held its own...its just getting to that point of either upgrading it or getting a new machine. Still running Snow Leopard as everything just works. Thoughts?