The value of watching old games for coaching?

How many you have memories of old but great teams? Ajax in the 70's, Brazil 1970 the list is could go on. But from a coaching point what is the value of watching these games?

I know you may all say "but the game has changed its not the same". But the point is how many tactical principles and systems can can be adapted to today's game if we made changes in line with speed of play, updated principles etc.

Rafa Benitez once made a comment about updating 80's Liverpool for the modern day game. I have to say he achieved at times a very effective style of functional play but nothing IMO close to that 80's team. Does this mean it can't be done? Not to me.

Louis Van Gaal adapted the pressing movements of Michels Ajax and 70's Dutch National team for his defensive system at AZ. He moved it down the pitch into AZ's own half and made it the base for counter attacks.

I always find value in watching old Milan games(I'm a fan of the Pressing game). I do think that these principles have helped me in refining some of my own methods. I would be interested to know how much value others get out of older games.