I think timestamps would be great especially reading logs when you get messages/requests in LS chat from other players and do not know when you got them. It would definitely help with organizing and promoting community. I cannot measure its value against the cost in system resources without knowing what that cost would be first. Having it generated local sounds good but I am uncertain what kind of exploits that might open up.

As for game play, it is very useful in timing actions and learning about the time cost of whatever your char is doing. Of course this is something that would make the game easier so people might not want that kind of advantage added. I have manually had to add my own time stamps via echo during game play and it is tedious but not horrible so I say soft yes with an indication that I would like to see other player's comments so I have an idea of what the down side is to adding time stamps vs not.