That article by Joel Spolsky was one of the few I can't fully agree with. The greatest successes of my career have often been in creating "next generation" implementations of software using newer or better technology and designs. Those re-implementations have resulted in very significant performance and productivity gains. While rewriting things from scratch can definitely be a naive impulse, there are times when it's the right way to improve a product, and if you fail to do so, your competitors will. The trend towards microservices tacitly recognizes this, I think; one of the tenets being it should take a small team a couple of weeks to rewrite any component of the system from scratch. When software was written poorly to begin with and has grown unmanageable by layering hack upon hack, it can pay to take a step back, look at the actual requirements, and consider if there's a better way.
I wholeheartedly agree with what you said. There is a time and a place for leaving legacy code alone. I also know from first hand experience some things are just too far down the hacky rabbit hole and you just gotta cut of the dead stuff and start over sometimes. But on the other hand, the only times I've done that in my career the code was written in a very anti-pattern style pretty much against all language guidelines and had hidden side effects everywhere. It was a mess to figure out how some features worked so I just rewrote some features in 1/10th of the time it took the original maintainer to piece in similar bug fixes in the legacy code.
