Vinland was never really a Norse colony in the same way that Iceland and Greenland were. Around 1000 CE, the Norse in Greenland made a handful of expeditions to Vinland over the course of a decade, none of which stayed very long - usually just making a winter camp before heading home again in the spring. After this, there may have been sporadic voyages to Markland (north of Vinland, perhaps Labrador) for quite a while, but again there were no permanent Norse settlements in the area. Some knowledge of Vinland worked its way back to Europe, but there it was generally thought of as just another Arctic island, like Iceland and Greenland. In fact, since the Vinland Sagas themselves weren't written down until more than 200 years after the expeditions, the oldest extant reference to Vinland is actually from The Deeds of the Bishops of Hamburg, which was written by the German historian Adam of Bremen around 1075. Adam of Bremen doesn't have much to say about Vinland, other than to mention it among the other northern islands discovered by Norse explorers.

There never really was a colony in "Vinland". What you are referring to is the Norse "colony" in Greenland. A settlement is by far a better word than a colony, since the inhabitants were politically independant.

The Norse were not writing at the time they were expanding. They minimally used runes, but they did not keep records. The earliest written sources about the settlement of Greenland come from Iceland and are written down in the 12th and 13th century.

As for the knowledge, absence of evidence is not evidence of absence. It is unlikely that those who frequently sailed in the North Atlantic had no knowlegde whatsoever of lands beyond Iceland/Greenland. It was always known in Iceland, Norway and Denmark that there had been settlements in Greenland.

Although Columbus "discovery" was not really a discovery, it still was a huge historical event from many perspectives. It was the first direct trip directly across the Atlantic. It had a huge cultural and economic meaning. It was the first lasting connection between European and American cultures.

In the high north, both Europeans and American natives were living on the edge of what was possible. The settlement in Greenland could not really survive without regular trading with the rest of Europe. The population was perhaps 2.000. On the American side, we had the Dorset Culture, whom very little is known about because the Thule culture drove them to extinction. Those cultures were both were spread and had limited contact further south to the rest of America.

The distance from Greenland to "Vinland" was also almost the same as the distance between Greenland and Norway. What was there to get which was not available in Norway.

About this, I know very little, but discovering America is not enough. You also need a financial powerhouse to fund expeditions and exploration. Technology in ship building matters. Navigational technique matters. Knowlegde of long distance trade matters. Did Europe really have these conditions for a long time before Colombus "discovered" America? Lets say someone would have sailed by the coast in 1250 and discovered todays Florida or the Caribbean. Would it really have been possible to built a significant post-Colombian connection at that time?