I definitely think Dundas is due for a renovation. Apart from those puke yellow tiles being absolutely awful, the additions since the last reno (escalators/walkway under the platforms, new Toronto Life and Dundas Square entrances), the station looks like a frankenstein of a bunch of different styles. A unified theme would certainly be nice.
Also, due to the fact that a) Dundas Square has become a prominent location, and b) it is the only station with the subway platform directly below street level, I always thought it would be cool if they installed a CN Tower-esque glass floor along the side of Dundas Square and/or the plaza spot in front of the Eaton Centre, directly over part of the platform. It would allow for natural light to enter the station, and it's not everyday you get to stand on top of where the subway is and actually SEE the subway beneath you. If it could be done in such a way that it's a mix of being structurally sound, artistically done, and plain old "that's pretty f'in cool", I think it would be a pretty big hit.
Just a thought.