Reparo is, according to HPWiki, a first-year spell. It flawlessly repairs anything non-magical, so long as it was not destroyed by powerful Dark magic. It seems worryingly overpowered in the hands of HJPEV. Apparently, if it is used on a wounded organism, it causes massive scarring - but of course, Hary doesn't necessarily see a living being, he sees a collection of water and carbon. If Harry could successfully do to Reparo as he did to Transfiguration (and assuming souls don't turn out to actually exist), he could not just resurrect Hermione, but also Merlin, or ancient Atlanteans. Matter really gets around - a bowl of water probably contains some molecules that were once in Merlin's brain. Perhaps the degree to which the target is scattered affects the magical power required, but that shouldn't be a problem for someone like Dumbledore or Quirrell.

EDIT: The wording of the spell doesn't specifically state that it flatly doesn't work on magical objects, but in the canon Book 7, the Mending Charm repairs a broken wand, but does not fully restore its magical functionality. A Reparo-resurrected wizard or witch would perhaps lose some or all magical capability (depending on how magic really works) but at least they wouldn't be dead any more. Also, it's not the magical abilities of ancient magic-users that counts, but rather their knowledge.