Case in point: the site we're looking at right now.
It's an opinion of course, but I personally find the hacker news design to be dreadfully ugly; yet it's one of the sites I visit and interact with the most frequently. It's simple and very usable. A flashy modern design might make it look better, but if not done well it might also impede functionality, and thus make me visit it less often. And the obvious lack of pretense is psychologically satisfying. Simple and ugly is fine if it's functional.
It's an opinion of course, but I personally find the hacker news design to be dreadfully ugly; yet it's one of the sites I visit and interact with the most frequently. It's simple and very usable. A flashy modern design might make it look better, but if not done well it might also impede functionality, and thus make me visit it less often. And the obvious lack of pretense is psychologically satisfying. Simple and ugly is fine if it's functional.