@ My 2p
"RAW image files are a few 10s of MB"
You're clearly not understanding. Take your 30MB RAW or even your 5MB JPEG. Open it in Photoshop. Apply some layers, some complex filters, etc. The original filesize is irrelevant - the final (unmerged) project can be some gigabytes, and takes many more of RAM while it's open. You benefit from more CPU cores, more RAM - and a 64-bit OS, with a 64-bit version of the program.
As to the whole 64-bit question, the driver and hardware support is long since here! I run an Asus P5Q with a Q9450 and 8GB DDR2. This is 2007's level of technology, and yet it's all perfect for (and uses) a 64-bit OS. Anyone who's bought a new machine or core components in at least the last 4-5 years should not even remember what a 32-bit OS is.
On the desktop, I don't know why they still sell them with 32-bit OS when there's absolutely no reason for it. On laptops, it's more understandable. I have a some years old dual-core Dell D620, and although it runs Windows 7, a 64-bit OS would actually be a detriment to it: addressing the extra memory registers would actually make a performance hit, while it's not physically capable of using > 4GB of RAM which would be the only real benefit at this stage. So there's an argument in there.
But seriously, on any desktop since 2006? There's just simply no reason for a 32-bit OS to even exist.