Of course by the time your wizard is third level, and has obtained knock (and web), your rogue is also third level, thereby making it a moot point. As previously mentioned, a third level rogue opens those chests just fine. And on a side note, if you sneek in, you can clean out the loot without waking up the bad guys. By the way, what do you need to open Brother Smyth's chest. THat was a no-go at fifth level for my rogue, so I'm going to try again now that I'm at six and have the masterwork tools.