To be blunt Neil Young would never join them on stage. They're the opening act and it would kinda ruin his intro. What I could see happening is Wilco (or Jeff Tweedy) joining Neil Young on stage at the end. That'd be neat. As for the 'Being There' block, the girl I was with had never heard of Wilco before and afterward she thought they were pretty alright.
That was my first time seeing Wilco, and they've been my favourite band for about six years. Needless to say I had insanely high expectations, but somehow they blew them away. Wow. And there's now a bootleg up at etree!