Ohjeh, now i have to write a longer clarification. It would be a cheap trick to say "read the word ‘mixed’’… But I wrote this a little bit provocative, so I think I have to suffer the consequence.
Yes, many of us “extremists” can look at a painting and can tell you by chance in witch quarter of the century it was painted, if it is from Italy, France, Northern Germany, Southern Germany… and we can tell you witch rank in the society the painted persons have, all by the clothes or armour.
The next thing you would say is, that those painting will not show the truth, but an idealistic imagination of the artist.
In return of that I would say: Artists in that period don’t do “art pour l’art” but would do commission painting for money. They are more craftsmen than artists. We can prove that they paint their everyday surrounding by comparing it with findings, legislative texts, by last will texts, by job-contracts etc. The trick is to filter out the fantasy elements, witch needs a little bit experience. But remember, many of us will do that for years, in their free time and for fun! 
Old clothes: In our time it is cool to wear clothes that shows us as rebels, as individualists… we like to look different from the other ones. In medieval times you would do everything to avoid this!
The late medieval society is mostly organized in very close and exclusive social groups. Each group has very strict rules and standards. That sounds bad in our modern ears, but in return those social groups are very important for living. They provide protection, social security, jobs, marriage and identification. It was very difficult to become part of such a group, if you were a stranger and if you would become an outsider, then you could easily fall through the social net and could lost your basis for living. The rules were so strict, they even had a written “dresscode” (Kleiderordnungen) by law!
Clothing were extremely important. As you say, clothes were expensive. In modern times we could hardly understand how important. Everybody can easily buy a new T-Shirt if you don’t like it any more, so clothes don’t really show who you are, because you could change them so easy. Imagine a society where you are forced by law (if you live in a town) or by social expectation what you have to wear! A new jacket costs you half of your income and if you decide to be “different” and wear what you want, you could lost your job and everything what you have! It’s even prohibited to wear clothes that are above your income and your social rank, so that everyone could see where you belongs!
Having all of this in mind, we could expect the clothes of a social group to be very homogenous.
Because “clothes make a man”, they are subject of important social mechanisms … and of fashion! You even won’t look more poor than your neighbor, but for a brave young man/woman fashion is a way to be a little bit different in your given boundaries… as long as it becomes standard, then everybody has to wear it and so on… but this process is not that fast as in modern times.
In large towns like Lübeck we had a whole street with “second hand shops” and an other street with tailors. If you got old cloth from your grandfather, then you go to a tailor (or your mother) and let them make something new from the fabric, because manpower is cheep and the fabric is expensive. In modern time it is the opposite!
For instance: If long tails on hoods are not in fashion any more, we could find hundreds of cut-of hood-tails in archeological excavations.
By the way, in medieval times not all clothes are made to last… shoes for instance were a “throw-away thing”. You would wear them for only some month. We found piles of shoes from that time with every excavation. So they are very easy to replace with more fashionable ones.
Soldiers: In modern times we think, soldiers should wear very comfort, sturdy, camouflage and practical uniforms. In late medieval times it was nearly the opposite! Professional soldiers don’t belong to any social group, they build their own and were free to wear what they want to show that they are different, what might be a universal need of men. So soldiers are the real “fashion-victims” of their time! They often wear impractical, colorful and exotic clothes and with this they often creates new trends.
Wow… very long writing! And for me it took a very long time to write it in English. To make a short ending: You will certainly found old fashioned clothes and armour among the medieval people. But everyone who could afford a little bit extra money (or do-it-yourselve time) would upgrade his look. So afaik it would not be the standard, but more the exception to wear old clothes.
Old armour: Of cause, there was much old armour in circulation. But because the same things like for clothes are true for armour (they are several texts where a poor guy in his fathers old armour was was the subject of mocking and jokes) you would like to get your hands on a new one as soon as you can. Because it is not only a fashion-thing, but also scientific progress, this is even more presumerable.
No. We do not see where is the quiver in the picture.
But this is possible where there is a lot of information. Those who engage in other periods, with much less information base, using the approach of the AK-47. 
