I pretty much agree with your song list, but I'd add Rider and Follow Me (따라와).
I agree that a collaboration stage with Rainbow would be awesome! I would give anything to see KARA perform A! And U Go Girl with Hyori too. They've done it before, but I think they can perform a more commanding version of this song now that they've matured more. And of course, their songs from when Kim Sunghee was still with KARA (I wasn't a fan yet, so I'm not too familiar). But it would be nice to have all 6 of them sing those songs.
And I don't know if the fans would appreciate it, but I personally would jump for joy if Junhyung were involved in one of Hara's special stages somehow...♥
...but honestly, they can sing whatever the hell they want. I just want them to finally have their solo concert!!