My first impressions from your question are that you seem to have a great many misconceptions about the Norse and their impact on Europe and the rest of the world.

Lets get the obvious stuff out of the way first. The Vikings were not a united force on their own. Many kings and other local powers were involved in raids, settlement, trading, and other things that the Vikings got up to. Scandinavia itself had kings in Sweden, Denmark, and Norway by the 11th century, Iceland is complicated.... but was ruled by a variety of local notables, and were independent from the other Scandinavian polities, for the time. While pre-Christian Scandinavia is nearly impossible to map out, there is clear evidence in the archeaological record for cultural differences between various Norse groups. Robin Fleming demonstrates this quite ably in describing the Norse encampments in England and the various burial practices that were attested during this occupation.

The particular instance of the "Great Heathen Army" or just Great Army, is a fascinating instance where a great deal of Scandinavians seem to have converged into one group, and tales of the Sons of Ragnarr Lothbrok aside, it is clearly worth mentioning that even in this case where there seems to have been a great deal of cooperation between Scandinavians of different origins, they were not one unified force.

Now what did the vikings actually do besides raid and marauder across the countryside?

I go into a great deal of detail on the varied activities that the Norse busied themselves with besides raiding monasteries in this thread

the tl;dr of that thread is that Norse activity across the North Sea, Europe, and into the Mediterranean world was primarily economic, and this took may forms. Raids are the most obvious example. However, mercenary work, trade, and settlement (linked with trade of course) were all undertaken by the Norse in this pursuit. In many of these regions that the Norse interacted heavily with, England, Normandy, and Russia, the Norse eventually arrived at local prominence and rule. The Kievan Rus and Normans are examples of this.

You mention, uniting of Europe in your question, and I think this is worth unpacking a little. At the height of the "Viking Age" (roughly from the raid on Lindisfarne to the Battle of Stamford bridge) Europe was really not united in any real sense of the word. The Carolingian Empire was disintegrating rapidly, Iberia was under the rule of the Moors, England was a patch work of small kingdoms, and so on.

While Norse activity did extend even into continental Europe at some points, the "unification" aspect of your questions is really only applicable to one area, England. In the course of Viking raids and attacks in the 9h century, all but one of the native English kingdoms was overwhelmed. The kingdom of Wessex eventually expanded into the Danelaw areas of England, and the descendants of Alfred the Great eventually crowned themselves King of England (specifically his grandson). As a part of Wessex's campaigns in Mercia and against the Danes England emerged from the Danelaw a united kingdom, that was subsequently conquered and traded hands quite a few times until William the Conqueror showed up. Here I think it is fair to talk of unification brought about by the vikings.

Now for the rest of your question. The end of the Viking era, again loosely defined at 1066, is many centuries off from even the earliest estimates of the "Renaissance" beginning, assuming you even believe that the Renaissance merits its own category of Western European history. However it should not be said the viking raids progressed or regressed Europe. Such ideas are far too simplistic to accurately describe the direction of history, it isn't a tide that comes in and recedes.

Now as for the "positive" aspects of the Viking depredations on Europe... It is very tricky. I am loathe to attach moralizing language to historical actions, especially those that were undertaken over one thousand years ago by people who are far removed from my own modern perspective. However with all of that said, we must keep in mind that for every viking raid or invasion there were hundreds or thousands of real people who were enslaved or killed as a result of the Norse showing up offshore. Rather instead the Norse and their impact on the world shouldn't be discussed of as positive or negative force on the world, but instead as a transformative one.

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Sources and further reading

I explicitly mentioned Robin Fleming's Britain after Rome which does talk about the archaeological record and what can be gleaned from it.

For more general sources, Peter Heather's Empires and Barbarians talks about this entire time period and the changes that were brought about at this time in world history, though it does start off more late Antiquity and only gradually progresses into the Viking Age.

I'd also recommend Gwyn Jones's A History of the Vikings if you want a more generic overview of the events of the Norse.