Videos made by random people aren't the same thing. Better in some respects - let's play videos show games comprehensively - but I don't think they properly replace the professionally made magazines which cover many topics and of opinions, have easily skippable ads and are more suitable to self-paced exploration.

I'm also concerned about not being able to run the software at all due to the complexity emulating modern systems (even for non-gaming applications) which rely on servers for functionality and licensing (DRM).

Are those Let's plays valuable because of games or because of personality of gamers?

If it comes to games, they have nearly 0 value and they can disappear - that would not change the value of the game, as they are derivative works and not the ones that are leaving influence. They have hardly any representation of culture around the game, and those who does not talk can be easily replaced with AI playthrough, so I would not care that much. Also, we are forgetting that gamers enjoy to discover new things - and those let's plays are there for a different reason - to stake a place of being there as the main source to generate income from ads and they are aimed at long investments, so they won't disappear as soon as I would like.