The good ideas taken from plan9 aren't isolated to it and could have been fostered outside of it, perhaps speeding up adoption of those ideas.
Everything you can do with Plan 9 you can do with any other system anyways, only it's marginally more tedious. If people can tolerate that, that's alright with me. What should I care how the masses do their computing? Why should I pester people about it? I don't go around arguing to people how great it is to be a pro-skub star-bellied sneech who eats their bread butter side down. Operating system evangelism and holy wars are older than the internet, and I have become very tired of them.