Some years back I have looked into the steam cleaning vacuums for the same reason. We have light uneven tile with light grout - yikes! The vacuums all seemed to fail the grout part, so I bought a Koblez Floor Scrubber and have been very happy with it. When I mentioned it back then to a co-worker, she mentioned that she had one for ages, so they seem to hold up well.
It does not steam, but the scrub brush kind of pounces up and down which gets in to the uneven spots and the grout.
Good luck with your search!