I agree most of your comments in relation to Ianto's dress sense in trying to woo his way into T3 but in relation to his suit at the end. I can't remember the exact interview but Gareth has stated before that Ianto is naturally more comfortable in suits, so not only is it that he looks like a T1 operative (which I found to be a great insight) but he is also 'himself'. So to me that was quite poignant as the way that Ianto finally got into T3 was to act like himself, the disagreeing with Jack, the little flirty side comments, coming up with a better plan and then catching Jack when Jack stuffs up.