Without trying to start a flame war, I completely disagree. I've been in the opposite situation: having a rental S while my wife's 3 was in the shop. I found the S to be a much less enjoyable driving experience. The front display was obscured by the steering wheel, the center console was overly complicated, the door trim was awkward, and not having the brake "Hold" when at a traffic stop (though I just may not have been able to figure out where to turn on that feature) were all major negatives compared to the 3. I don't consider the 3 interior "plain", but rather simplified, which I like. I'm sure we both have some bias based on what we're used to driving.
Regarding space in the Y, I don't think you'll feel so cramped. I have a 3 and my wife upgraded to a Y, and the difference in space is significant. That's one of the reasons I plan on upgrading mine as well.