Wouldn't that depend on how the game has gone? I mean, conceivably, if the "top two" civs are neck and neck, then domination of the new world would be pretty critical. Plus, there's a wealth of resources to be utilized and, because the barbarians have actually developed cities at this point, there's plenty of places to establish a base of operations.
I mean, if you're so far ahead in tech that you don't really NEED the new world and you're going for space victory, no big deal. If you're going for cultural and you're clearly winning that too, it's not as big a deal either. But if you're going for domination or diplomatic win, the new world can be pretty crucial.
Right now, on the Terra map I'm playing, I've got a tech lead and just circumnavigated the globe two turns ago. I've got galleons and will soon have Redcoats to begin capturing and/or establishing cities in the new world. My existing cities are well developed enough by now that I can focus more on specialization through building wealth, research, and/or culture, while other cities will purely crank out units for my expansion. I've even got a forbidden palace waiting to be built on the new continent.
The other civs have caravels and are exploring right now, but I intend to be invading ASAP. It's currently about 1570 or so in an Epic game, too, so there's still PLENTY of time left to play. Plus, Musa Mansa has been a thorn in my side as far as tech racing is concerned, so establishing colonies overseas will definitely help me. He's currently about 100-ish points behind me, but that can be made up relatively quickly if I'm not careful.
So, yeah, you can ignore it sometimes, but if it's a relatively close game, it can help to take advantage of it.