I would like to correct this, because it is not correct.
There are two reasons that if you have a 64 bit computer, 64 bit applications are faster.
First, programs compiled to 64 bit can usually be made to run faster on 64 bit CPUs than 32 bit programs can be made to run on 32 bit CPUs. This is even before considering that if the software is memory intensive, then it will run far, far faster in 64 bit.
Second, on a 64 bit Windows computer, 32 bit applications have to run in a 32 bit CPU emulation mode. It's really more of a thin compatibility layer than a big-time emulator, but there is usually still a performance hit involved.
From Microsoft, "Running 32-bit Applications" --
"WOW64 is the x86 emulator that allows 32-bit Windows-based applications to run seamlessly on 64-bit Windows."
They usually run seamlessly, but also more slowly. How much more slowly depends on the application, what it's doing, and also on the 64 bit chip that is installed (emulating on an Itanium is slower, for instance). In addition to the slowdown because of the conversion/emulation, the emulator itself takes up some address space and CPU time, which may limit for instance the number of threads.
There is an upside: "WOW64 enables 32-bit applications to take advantage of the 64-bit kernel. Therefore, 32-bit applications can use a larger number of kernel handles and window handles."
See also from the PVS-Studio blog, "Why do 64-bit applications work faster than 32-bit ones?"
Microsoft is even working on an emulator that allows x86 Windows applications to run on ARM-based devices, like the ones that Smartphones use. That's a much bigger task of emulation since the instructions are totally different.
Anyway, it's not true that there is no reason to switch to Office 64. On the contrary, if you have a 64 bit machine, and do not require 32 bit plugins -- although most Office plugins have been converted to work as 64 bit -- then there is no reason not to switch to the 64 bit version. It will be faster out of the gate, and if do you need to work with large files, then it will be magnitudes faster. It's even likely that at some point in the future, developers will stop supporting the old 32 bit plugins, which is already the case for some Photoshop plugins.
If you do upgrade your computer from 32 bit to 64 bit but keep running 32 bit applications, you may be disappointed in your upgrade because it's actually possible that some applications will run slower than they did before, on the 32 bit computer for which they were optimized.
It's true though that plugins are one of the big impediments for applications switching over to 64 bit. This was maybe most notoriously true for Photoshop and for Office, but most plugins for those have been available in 64 bit for awhile now. Evernote may often be less processor-intensive than those but running applications as 32 bit on a 64 bit computer will still less efficient and will use some resources for CPU emulation.
SpankyJ on the Microsoft Developer blog explains why 64 bit applications cannot use 32 bit plugins: "It is important to understand that once you’re loaded up in the WOW64 you’re a 32bit process and there’s no turning back. You have to use 32bit dlls all around. On the other hand, once you start up 64bit you’re 64bit, no 32bit dlls allowed."
One hacky solution that works for Photoshop is to use a 64 bit plugin that is a wrapper for 32 bit plugins. There are a couple of those available, but I don't know if that approach would work with the 32 bit plugins for Evernote. I doubt it, since Photoshop plugins tend to go off on their own and work with an image, while Evernote plugins are more tied into the user experience.
p.s. In this forum editor, I tried to use letters like "a)" and "b)", but it converts "b)" into a smiley with sunglasses...which is a little bit annoying...