I despise Rey. You ask how to tone down the Superman push that Rey is almost always on? I would say book him realistically. For as much crap as Cena gets, his victories are more realistic than Rey's. Currently, Cena is working his way towards beating the Nexus, but even he has to have a team to do it. Quickest way to get rid of the Nexus? Move Mysterio over to Raw and have him take them on. Then there's no way that Team WWE will lose.
It may be because I dislike him, but he doesn't seem to have any legitimacy in the main event scene on Smackdown. He made Swagger look bad when he beat him despite having an injured ankle. If Big Show were a heel, he would lose as well, despite his size.
In addition, I don't like the backstage politics. If I remember right, he made a stink last year when he was suspended for violating the wellness policy. I think he was unhappy when the WWE wouldn't let him make an appearance for AAA, even though I can understand the WWE being unwilling to allow a performer to wrestle for another promotion. He didn't want to lose the IC title to Dolph Ziggler and only lost it because he got suspended, and not to Ziggler, but to Morrison.
He's also injured several performers lately, namely the Undertaker, who was supposed to have a part in this years Summerslam but has instead been healing the broken orbital bone he received.
And, this may just be me, but while I understand the WWE wanting to market to the Hispanic demographic with Rey, it annoys me to no end when he cuts promos in Spanish. Maybe it's just because I can't understand it, but it doesn't seem like there's any actual need to do that other than to just pander to the audience.
Again, if I remember right, I think there were rumors that he was thinking of asking for his release, or not renewing when his contract expired. I think it would hurt the WWE financially, but I don't really want to see him pushing over everyone on Smackdown anymore.
I know I've bashed Rey, and I could be wrong on some of this, but I am willing to hear counter-arguments. Nothing I've read makes Rey seem like he's an asset from anything other than a financial standpoint. However, I'm definitely willing to hear differing opinions.