I agree that Vinland is never going to be a refugee colony or anything.
However, if Scandinavian internal politics had been just a bit more volatile, and Europe/England been a bit tougher of a nut, there's the possibility of a few Jarls taking expeditions farther afield, not the least of which is to actually get out from under Monarchal rule. I mean, you might technically be a vassal of the King in Vinland....but he sure as heck isn't coming out there in force to change your mind on anything. You're effectively on your own.
I think the issue we run into is a combination of the Norse propensity for dealing with conflict rather decisively, which hurts them diplomatically with the natives. If they manage to meet a tribe that's impressed by their advances and is small enough to pose no legitimate threat, AND they manage to keep things diplomatic for at least the first century with said tribe (though maybe fighting rival tribes as an ally), then there's a reasonable chance that they get enough population on hand to make a going colony. Actually allying themselves with a native tribe, while requiring a bit of a suspension of disbelief all things considered, would be really useful for the Norse. They get some guaranteed borders at least in one area, they get trade, especially in trade goods and foodstuffs in exchange for metalworking and such. They also get access to knowledge about navigation in the local area. The Norse real advantage is Naval, something that the locals just don't do very well.
The 400 person colony size works for something like Iceland, which has for practical purposes no native population to compete with. I think that Vinland needs 1000 population to tip over that scale into being a 'sustainable colony'. I'm basing this on about 10 percent of a population being practical for military purposes, with 25 percent in time of great emergency. I think that to deal with native troubles and keep secure, the Vinland colonists would need a standing force of around 100 under the Jarl, and anticipating that another 150 or so of the colonists would be able to grab spear and shield and give a decent accounting of themselves. With the Vinlanders having a technological edge, that should be enough to protect the colony, and maybe prosecute some proxy wars and such with an allied native tribe.
What I see in 200 years, or about the time of the Little Ice Age, in this 'ideal scenario' Vinland is the following:
Alliance with one native tribe, maybe occasional proxy wars and such where the Vinlander shield wall is known as a bit of an 'elite force' in land combat and the Vinlanders and their natives really become a local Naval power using the availability of lumber to build a good number of ships in the area, and with no real competition from the canoe oriented natives.
Multiple palisaded settlements along a river or the coast, probably 1 major settlement with 3 smaller ones or so. Local focus is on forestry and fishing, with agriculture and herding a smaller concern that'll take another couple of hard centuries to build up, probably herds before farming with the Little Ice Age getting involved.
Trade with Norway through Greenland/Iceland, with some additional colonists making the journey, but we're talking a trickle of a ship every couple or three years with maybe a couple of families tops, probably more likely individuals and traders. With Norse decline, this might bump up a bit as there's room for expansion and while Europe might have everything, room and land is a problem.
There will be native troubles by this point, but with a relatively well established colony and a native ally of several generations, the Vinlanders might be able to really lock down their territory and even bring the European style of war to the hostile tribe, crushing it in decisive riverine raids using their supremacy on the water and destroying villages. Defensively the Vinlanders would have the advantage of European knowledge of defensive works, and the pre-planning of good palisades and such.
A threat moving into the 1300s IMHO to this theoretical super-colony would be that the King would want to assert control. I'd see Vinland as developing its own identity and not wanting to be considered a vassal state. And with their distance from Norway or Denmark, it's likely that they could maintain their de facto independence, as an invasion fleet to re-establish royal authority would have one heck of a long voyage.
By the time that the Spanish are looking down South, there's already an established 'country' in the new world. Small, but established, with its own structures in place. I see by the mid 1500s a nation of Vinland with a population of 5000 or so, and then with the age of Exploration and colonization coming about, and the Reformation and such causing various groups to Exodus from Europe, AND naval advancements allowing for better and safer voyages, Vinland gets a new influx of various northern european settlers and by the time of the serious English Colonies in the 1620s or so you have a nation of Vinland with around 10-15k population running along the coast from Nova Scotia and Prince Edward Island to Newfoundland.