Heaps of things to take into consideration here!
Was the wheel balancing and alignment done correctly, by a reputable person?
Hit any gutters or large potholes recently?
If you rims have any imperfections, balancing can only correct these to an extent, there can still be imperfections.
I once bent a rim on a previous car via a pothole and found that when I changed my tyres shortly after, I could only put it on the back due to it being rough even after a re-balance. If it was on the front you could still feel the slight twitch through the steering wheel.
once I managed to find a new rim I got rid of the other completely.
As others have said theres other steering components, none of which should be worn being an 05 model, but if you've hit something these parts could definately be affected. This could also be something as simple as going over a speed hump or even a dip too fast.
Hope this helps a little.