I’ve never seen any actual metrics on it that weren’t pseudoscience at best. If you have some I would genuinely like to see them.

From my anecdotal experience YAGNI and making sure it’s easy to delete everything is the only way to build lasting maintainability in software. All those fancy methods like SOLID, DRY, XP are basically just invitations for building complexity you’ll never actually need. Not that you can really say that something like XP is all wrong, nothing about it is bad. It’s just that nothing about it is good without extreme moderation either.

I guess it depends on where you work. If it’s for customers or a business, then I think you should just get things out there. Running into scalability issues is good, it means you’ve made it further than 95% of all software projects.