Ahhhh, excellent question that I can't answer well.
I can answer you from what I know, and what the various sales pitches I encounter. For the record, I have a Lenovo X-61 with a Centrino Pro which is a dual processor (and this is the point where Vista 64 comes in), but I run Vista 32 and the RAM is full at 4.
The deal with Vista 64 was it was supposed to be that it allowed your dual processors in true parallel fashion so you basically had two computers running and you could have two applications running side by side without sharing resources slowing each other down. A feat which XP64 was not capable of. However, the manufacturers of ancillary equipment did/do not have the drivers for operating in the 64 bit mode, so they also built a 32bit, which was the prior standard and has been for several years, version which due to some of the equipment I have to hook up to, I have to use. It's a bit disappointing really not to be able to make full function of the processor since I often will be running navigation programs and Photoshop, or satellite internet and surfing/downloading/.... However, things are coming around and more stuff has the 64 biut drivers. The having to buy new printers and such, thats not that big of an issue to me since they rarely last as long as an operating system. My computers only last a year or so, but hopefully this one will do much better. I'll probably augment it with another computer later this year,
not sure if larger or smaller. Can you run a monitor WiFi or Bluetooth?
Anyway, that's the deal as I see it, but I'm like you with computers, I'm an end user, that's it. I will do physical repairs as turning screws is turning screws regardless of what you're turning on, but I am in no way a "techie".
The information above is my view based on my actual (fruitless) experience trying to use Vista64, and I have one other issue that I'm not sure is a Vista problem but when I close a Flash player like from a CNN video, IE & Firefox would crash. So far, Google Chrome has been exceptionally stable. Oh, also after being on for a few days it may develop a USB issue that requires a reboot.