You can use "system connections" so your wifi doesn't go down when switching between users, it works for me (I have a mix of kubuntu and ubuntu machines). I find it strange that nm-applet crashes, did you submit a bug report?
My experience isn't that nm-applet crashes when you switch users, but the icon is no longer available. What that means is that, if user A is the first to sign in, nm-applet runs in their taskbar. If you then switch to user B without logging out, user B cannot switch networks or other settings without doing the kill/restart from the command line because the applet is not visible. For something like network settings on a desktop OS, this is nearly unacceptable and a royal pain in the ass.