Although your right about it being in the threadlistings already it doesn't hurt to have it previewed in the tooltip. You can think of the membercard being the same, your essentially clicking the members avatar yet you know the person avatar you clicked yet it shows in the membercard.
I don't see anything wrong with the avatar being in thread preview listing. I just wish there was an on-off switch for it in style properties for styles that you want to create that you don't want avatars to show up a lot in. but wait... actually I can create an addon using your code so that you can turn it off in style properties. nah I'm straight.