Ya know, you'd be even more dangerous taking 4 levels of warlock instead of wizard.
You'd get:
-> a weak ray attack (2d6)
-> Detect Magic at will
-> 3 Invocations (How about any 3 of these: Spider Climb at will, See Invisible at will, something to make you harder to hit at range, make you untrackable AND unscenatable, Shatter at will, +6 to Diplomacy, Bluff and Intimidate, +6 to Tumble, Jump and Balance)
-> Damage reduction 1/Cold Iron
-> Take 10 on UMD checks
That would complement your rogue quite well I'm thinking
Edit: added a few details I missed earlier.
Oh how I love the Warlock class