I believe you underestimate the amount of good posts. There are many people posting personal stuff about their daily lives. There are many people posting art and stories they created. The original stuff is there. I tend to post on information I am interested in. I have used Wikipedia as a reference...cited of course. I try to draw in as many resources and links as I can, as I don't want to be discredited.
"What can be asserted without evidence can be dismissed without evidence" Hitchen's Razor
There is no problem with Wiki, Wiki is a great source. I use it for some facts.
The key element is the additional value of the post in comparison to Wiki.
Take the Wiki page --> Rephrase --> Rubbish
Take the Wiki page --> Expand something --> add remark --> take something from outside source --> take more Wiki --> Great! You made the post better than Wiki, the additional value