Do 64bit software/applications require more RAM than their 32bit counterparts

Stick with the 64bit. 32bit is a dying breed. There is no doubt in my mind that Logitech supports 64bit. Make sure you have their latest official drivers installed.

That .5gb of ram may not seem like much now, but you will be kicking yourself later for reverting to 32bit.

I don't have any special information about the upgrade advisor, but here are a couple possibilities:

1. There's not much reason to use 64-bit unless you're going to have more than 3GB of RAM, as the extra address space won't do much for you. There are some special-case reasons, like high security applications or certain media processing, but in general memory address space is the reason to use a 64-bit OS at the moment.

2. 64-bit OSes DO use more space to store memory addresses, as each address is generally twice as long (this isn't totally precise, but a generalization here will do). This means that storing the locations of data in memory takes more memory itself. Again, however, this isn't really a reason not to use a 64-bit OS, because if you are using one you are probably taking advantage of its increased address space anyway with a decent amount of RAM.