A point I forgot to mention before. When determining how awed/surprised people are by something, I like to use the "level rareness" guide. In 3E, I use this one, based on the "Aragorn was 5th level" article, although in 4E the numbers would obviously be different:
Level 1 - Common.
Level 2 - Semi-Common.
Level 3 - Rarer, but not unheard of.
Level 4 - Rare, not many around.
Level 5 - Very rare, almost unheard of.
Level 6 - Legendary.
So a spell you can cast at 1st level, is probably not going to baffle people. If you blast someone with Magic Missile, the bystanders aren't going to say "What just happened? There's no weapon!!", they're going to say "Call the guard, that mage just killed someone!".
A spell available at 3rd level, like Invisibility, is going to be somewhat more surprising to the general populace, but in a town of any size there will be people who know what's going on. Maybe the bystanders have no idea how the gems were stolen, but when the guard is called in, they start looking for signs of an invisible thief.
A spell available at 5th level, like Clairvoyance, is not something many people know about or know how to deal with, but the "big players" - leaders of cities, head of powerful guilds, armies of kingdoms - are prepared for it, and will take appropriate measures like shielded rooms for important meetings.
Higher level spells are going to be beyond what most people know. You've got to be a bit legendary yourself - or at least have advisors with that knowledge - to be prepared for them. (This applies more to "physics bending" spells than standard blasting spells).