You can buy two used 5D MK II's for the price of a used 1Ds MK III. The images will be almost identical, only the build and AF / Shutter are the different things that matter.
If you need to use your camera under difficult conditiond, rain, cold, or dust, you might prefer the 1Ds, for the average wedding shooter, having two 5D MK II's would be best, or, if you already have a backup, pocket the $$ or buy a new lens.