"Safety is the number one priority but...." belongs in the same stash of rhetorical devices as "I'm not a racist or anything but..."
I'd say "over-cautious" was probably an oxymoron, especially in a field of operation with as many variables and natural hazards as aviation, and in a situation with as many unknowns as this ash predicament.
One day the actions of the authorities over the last week might be legitimately criticised as unnecessary - but that will require a fair bit more hindsight than we currently have. We're still in a phase where damage to engines - significant enough to reduce maintenance life if not actually precipitate accidents - could be occurring, and I think a little circumspection and humility amongst aviators is the order of the day.
If it turns out to have been a massive overreaction, then I still say that when you make a mistake it's better to have the ugly numbers for "losses" in the £s/$s column than in the one for human beings. Governments can't win in matters like this - better to be hated for costing money than costing lives.