Er, what? Grem, are you trolling?
I kinda like the twilight. It's pretty. And it sets a dark mood, if you're eveil, but it's hard to stay evil after defeating Nemesis.
But I have played for 100+ hours after the perpetual sunset kicks in in one of my profiles, until I had covered almost the entire land in cities. So no, it doesn't lead you on an eventual path of defeat (you've already won, how can you lose?!), nor does it mess up your profile. It can get boring, though, which is why you keep another profile, do skirmishes, or just start over and keep your creature.