Over-engineering, architecture astronauts, hurt a system a lot more than someone following YAGNI. Making systems that are a big mess of hard to understand and modify code (even worse). I've seen this happen again and again.
Architects sitting in ivory towers pump out Word documents which result in overly complicated systems. Large, slow, waste people's time and money. The whole idea of "oh, in 10 years we may want to handle this and that" adds unecessary code which then needs to be tested and creates many more points of failure. And did I mention slow? These hairy-balled monstrosities are terribly sow.
If over-engirneers got paid by the line of code, they'd be millionaires. If they got paid for writing elegant, short and easy to maintain code, then they wouldn't have two pennies to rub together -- the YAGNI developer would be sitting in his yacht.
You Ain't Gonna Need It!