Quote Originally Posted by Sephiroth
This was an itinerant race. They would migrate in, settle the Planet, then move on… At the end of their harsh, hard journey, they would find the Promised Land and supreme happiness.
Xurts, I'm afraid you're wrong. This is exactly, word for word, what Sephiroth said in FFVII. Though he never specifically says "travel from planet to planet" he does say settle the Planet then move on. This pretty much says that they had some means of traveling from planet to planet. Perhaps not space travel, but some deep magic that they could use. Not really sure.

But basically, they did inhabit several planets and continued their journey until they found their own Promised Land. Since this is different for everyone, I'm sure that there are lots of people who stopped along the way and said, "this is it for me. My journey is over." This is supported by what Sephiroth says next.
Quote Originally Posted by Sephiroth
But, those who stopped their migrations built shelters and elected to lead an easier life. They took that which the Cetra and the planet had made without giving back one whit in return!
Now, of course at this point he is bastardizing what it was that they really did to make himself seem more justified in his actions, but basically this means that there were some who stopped at Gaia and decided that this was there Promised Land and thus ended their journey.

In fact, the game also makes mention of a "small group" of them fighting Jenova. Well, I'd imagine that it was a small group because quite a few of the Cetra continued their journey, leaving those who wanted to stay behind. So, the Promised Land is obviously something besides the Lifestream. It can be a way to the it, but it is not neccessarily the Promised Land.