I've vaguely skimmed over this thread but I feel the need to speak my stance.
As others have said we don't watch lets plays to only watch the video game. The personality that is playing it is the reason I watch. I recently watched "NothernLions" lets play of Terraria, all 31 episodes(each of which were around 15 minutes long) . But at the end of it he was overpowered and pretty much bored with the game. But after watching I knew I wanted to play, so I got the game.
"we" you didn't asked me for sure, because i'm not included in your "we".
I use lets play on youtube video's to experience the game, so i don't have the need to buy it. It saves me money and time.
I do have preferences for different youtubers / livestreams, because some tend to completely destroy cutscenes that progresses story's in games by talking constantly through it, while others are silenced and just let me watch it on the level i like to watch it. The game is the main reason why i watch, not the person that plays the game.
The fact that every new game "even playstation 4 and xbox one games" are live streamed on day one and completed on the same day by a lot of live streamers ( games ). Makes the need to invest in these consoles or buy those games for me useless.
I got the feeling atm, that i owned a ps3/xbox360/wii/ps4/xbox one. But i never have touched any of them. Reason? youtube ( for older games ) and livestreams for brand new games.
I was standing lately infront of a shop where a PS3 was sold with a ton of games that would be interesting towards me for cheap, but i decided against it because i already had the feeling that i played them. And if i want to experience them again, i can just youtube it instantly.
But it's not just limited to console games, also towards PC games, handheld games ( pretty much anything game related ).
The only games i do buy are heavy focused multiplayer games or gameplay focused games without much story if any at all. Because youtube/live streams don't really work for them.
So for a person like me, these company's do lose a lot of money.