To be honest, I've purposely left out crop lenses as it didn't make sense to me at the time to have lenses that I could only use on one of my camera bodies. But to answer your question, I am using the same FF lenses I do on the other bodies, which would normally consist of the following:
70-200 2.8 II
Given that, would you still think it makes sense to trade down from the 7D to the 5D? Not sure I want to change my lens lineup or add crop lenses to mix just for the sake of the 7D.
Your lens collection alone probably will make that decision for you. Also, if your primary work is wedding, and you have the 1D3 (APSH crop) to saddle up with the 5D2, then it makes sense to move to the 5D as a backup to the backup, as you already have 2 great tools at this point.
You do lose high ISO and you lose the ability to share batteries with your 5D2 though, and you don't get micro adjustment (which may not even be needed on the older camera). One last thing to consider is you are down to just one camera that shoots HD video.