Since you didn't specify a specific part of the medieval world, I can answer with one specific example of post-combat-looting from a topic I know a bit about; the Catalan Almogavers (mercenaries), and the Catalan expedition to the East.

 

(Note: All of the information in this answer is based directly from a primary source on the matter; the chronicles of Ramon Muntaner, who was actually one of the leaders of the company. At the end of my post I have a citation for the translation I quote from)

 

First, as a bit of background; the Catalan Almogavers were essentially mercenary companies of shock infantry made up of soldiers from the Crown of Aragon (most of the men in this group were Aragonese or Catalan). There were many groups of Almogavers, but the group I'll discuss here is often called the great/grand Catalan company.

After the war of the Sicilian Vespers, the company, led by Roger de Flor took up service under the Byzantines to combat different Turkish groups in Anatolia. After finding great success, the Byzantines betrayed the group and had some of the group's leaders (including Roger de Flor) assassinated.

This led to a series of intense battles between Byzantine forces and the greatly outnumbered Catalan Company.

 

Luckily for us, one of the men in the Catalan company was Ramon Muntaner, who beyond being one of the group's leaders, was also the main man in charge of the treasury and book-keeping of the company. Even more luckily for the purpose of being able to write this answer, he is also considered to be one of the Crown of Aragon's most important chroniclers and chronicled much of the company's exploits.

In describing his role around the time of the biggest battles between the company and the Byzantines:

"I was also Chancellor and Treasurer of the army, and the army scribes were always by my side, so nobody but I knew how many there were in the army at any particular time. And I kept written records of how much each man received for a fully-armoured or lightly-armoured horse and for foot-soldiers likewise, in such manner that the spoils from the raids had to be divided up according to my book; from which raids, whether at sea or on land, I [meaning the treasury of the company] retained the fifth share." (pg. 99)

Robert D. Hughes, the translator of the text I'm citing, adds in a footnote that what this meant is that the other four fifths of the loot was kept by those who had earned it.

 

So then, how much loot did the Catalan Company earn? From what Muntaner describes, a lot.

 

Take for example the first major battle between the Catalan Company and the Imperial army. Muntaner does not give an exact number for the amount of men the company had in this battle, but from an entry a bit before the battle he had described a number of 1,462 (with 206 being horsemen). The first host of Imperial troops is described to have consisted of "at least ten thousand horsemen and a good thirty thousand foot-soldiers" (pg. 74). Muntaner describes the company as essentially driving them back repeatedly, until the Imperial army routed, at which point the Company chased them down in a slaughter for 24 miles (pg. 85).

Muntaner claims that from this battle, they killed "a good six thousand horsemen and more than twenty thousand foot-soldiers."

 

As a non-expert in general medieval warfare myself, I don't know how embellished these numbers might be, but in any case, Muntaner makes it clear that the amount of loot gained from this battle was massive in comparison to the relatively meager amount of men they had with their company:

"What can I tell you? The gains that we made from that battle were so immense that they were beyond reckoning, for it too us a week to gather up the spoils. We needed only to remove gold and silver, since all the horsemen's belts and the swords and the saddles and the bridle-bits and all their armour were garnished with gold. And all of the there had been carrying money, the foot-soldiers likewise, and so the spoils were endless." (pg. 85)

He goes on to describe that they also "took a good three thousand horses that had survived... Thus we had so many horses that there were three for each one of us. " (pg. 85)

 

Regardless of whether or not you believe the amounts of casualties listed by Muntaner, clearly the Company was well-endowed with wealth after this battle, and more like it followed. A brief description of the following major battle (also a win for the Company) reads: "And we gathered up the spoils, taking away with us a good ten thousand carts - each of which was pulled by four buffaloes - and so much livestock that they covered the entire countryside. We had acquired countless spoils, much more than in the first battle." (pg. 88)

Now while Muntaner doesn't give exact numbers in terms of how much loot exactly the average soldier gained in these battles, it's clear that the amount of loot flowing into the party was an immense amount; Muntaner points out that in horses alone, the amount they gained made it so that they had almost 3 horses for every fighting man (not that all men would necessarily be mounted in combat, but it still gives an idea of the wealth that the company gained).

 

All that to say, that at least in the case of this particular mercenary company, the soldiers did get very rich from the loot. As far as your more specific questions concerning levied peasants, I have no knowledge, but I hopefully you find these excerpts from Muntaner's chronicle at least a bit interesting or insightful. I am not a historian myself but this is one of the few areas where I've read several sources, and your question brought this to mind.

Source: The Catalan Expedition to the East: from the Chronicle of Ramon Muntaner, translated by Robert D. Hughes, with an introduction by J. N. Hillgarth. Barcino/Tamesis, 2006.

Edit 1: Formatting for readability.

Edit 2: As people have pointed out, this doesn't really answer every part of the question. This is only one specific example, and even this example is lacking concrete records and exact numbers for how wealthy these soldiers would've been from their conquests. My hope is that it at least gives an idea of what a looting policy could look like for an army of medieval mercenaries, even if the numbers involved are almost certainly exaggerated by Muntaner. Beyond that, while I'm sure there are better examples, I thought that without any other answers I'd at least try share something tangentially/partially related that I do happen to know a bit about.