I just recently bought a 27" i3. Let's say my needs change or I just want to get the latest & greatest. Would it make sense for me to get a new processor & graphics card (& whatever else) instead of buying a new iMac? I always hear about people getting new iMacs when upgrades come out, but what about buying replacement parts to enhance your machine? Is that a common practice? Just curious if it's something I should consider when the time comes.