I'm not sure if it's because I'm "used" to Eliezer's styles, but while I can recognize the two posts use different styles, both seem equally "appealing to read" to me. That said, I feel more "informed" and "convinced" by the 2009 style. One thing that really struck out to me as a difference between the two was that the 2009 explored more deeply the school principal example. Before reading the 2009 essay, I "believed in" the claim "It doesn't matter who started it; the important thing is to end it". I don't think the 2006 essay would have convinced me that this claim was false, but the 2009 sure did.

Unfortunately, this probably has a lot more to do with difference content than in styles, so I guess this might not be the most useful datapoint to use in your comparison.

Why would I care about whether the Superhappies change themselves to appreciate literature or beauty? What I want is for them to not change me.

The bargain that the Superhappies are offering is to change you less than if they had just changed you by force. I'm guessing if the humans didn't agree to the deal, the Superhappies would have either exterminated the humans completely, or convert them completely to superhappy values.

The benefit of Superhappies changing themselves to appreciate literature and beauty is that when they convert you, you get to keep the part of you that appreciated literature and beauty.

All their "fair-mindedness" does is guarantee that I will be changed again, also against my will, the next time they encounter strangers.

Actually, it won't be against your will, because you will have had the same values as them (you're all merged now, remember?)

"Just as they would regret not eating the tiny bodies of the infants." is one of the more moving passages I've read in a long time. Well done Eliezer.