I'm pretty happy with my gear, although I am upgrading my amp and DVD player very soon. There is equipment out there that I can't afford and probably sounds better, but at the same time, I've heard enough rigs that are a lot more expensive than mine, and don't sound nearly as good.
Some people become lifers with certain brands - (McIntosh, Naim...). I think these people have met their grail sound. But most others keep hunting. I may have found my grail speakers, but it's only been about 3 years since I first bought them, so time will tell. Also, with some new gear feeding them, I'll have a better idea if I need a change. I do know, that with my new DAC, the system improved a lot, and although I thought it was the speakers, it was not.
Part of the pursuit isn't necessarily something better, but just different. Some people switch from tubes to solid state, monitors to floorstanders and back to monitors again - it's fun to experiment.