MacOS – Spotlight is broken on the main partition in OS X 10.7.4

Not long after updating my main OS X installation from Snow Leopard to Lion, Spotlight stopped working on that partition, and I'm desparately trying to get it working again. It will find no files for any search, though it is working normally for other partitions and network volumes.

I'm running OS X 10.7.4 on an early 2009 Mac Pro. My main partition is 1 TB, and at about 75% capacity.

For what it's worth, I remember this started shortly after I installed a developer preview of Mountain Lion, but that could be a coincidence.

'mdutil -s /' prints the following:

/:
    No index.

I've tried many, many things to fix this problem, and all of them have been unsucessful. They are:

• Repaired disk permissions

• fsck'd my main drive

• double checked that in Spotlight Privacy preferences my system volume wasn't excluded

• Tried 'sudo mdutil -E /' but it prints:

  /:
      No index.
  

• Tried 'sudo mdutil -i on /' but it prints:

  /:
  Error: unable to perform operation.  (-400)
      No index.
  

• Other people who got the -400 error reported that terminating all mdworker processes and quickly recursively deleting /.Spotlight-V100 would fix it, but I tried that (several times) and it didn't resolve the error.

• Ran my drive through DiskWarrior

Also, importantly:

• I reinstalled Lion using Lion Recovery (not a fresh installation), which fixed Spotlight for about a day or two, and then it became broken again in exactly the same way.

I'm totally out of ideas on how to fix this problem. I could resort to installing OS X fresh to a blank partition, but it would take hours and hours to migrate all of my data, settings, scripts, tweaks, and to reinstall all of my professional software. I really don't want to have to do that.

Any help would be greatly appreciated!