Nandroid backup does backup your ril as the ril is residing in /system/lib. So if u are restoring a nandroid backup, you will restore the ril in that backup too.
actually u don't need to wipe the cache. And regarding he procedure, after u smartflash, make sure u start the phone it at least once, then restore nandroid. Usually u don't need to get the RIL again, because as far as i know nandroid backup doesn't backup RIL. But if using LG GetRIL and u get wrong RIL, u can always download and install RIL through this app. Mine is fine using this procedure. I didn't do any wipes.