Earlier quoted context omitted.
With current ram sizes this might be negligible, but 32bit chrome would have to load 32bit versions of all system frameworks, while you have 64bit in memory all the time. The less 32bit apps you have, the better :)
I imagine this might affect startup times too? I.e. you are likely to have the 64bit frameworks already in memory while you have to load 32bit from disk when starting chrome. (Chrome startup is so slow on my machine that this might be negligible anyway).
Yes you're right. At the same time, you probably have some other 32bit apps that forced those libs to load, e.g. Dropbox, which is still 32bit and starts with the system.