One good reason for a wizard to take at least one level of Rogue - it gives you lots of skills that you can spend your skill points on. They may be cross class, but your skill cap becomes level+3 instead of half that... A wizard has lots of INT, once you've got your concentration and spellcraft, a human rog1/wizx with an 18 INT would have 5 skill points left over - enough to keep spot and hide maxed out, for instance. Or how about spot and pickpocket, but the latter used for "sleight of hand" to get at hidden material components (could be a cool idea!)
Cheers