Attracting Vanity Users for a Social Network

I am a regular user of Social network like FaceBook,Orkut, LinkedIn.

Collaborative Knowledge Sharing Networks Like Wikipedia , WikiQuote,Del.icio.us

Q&A forums like USENET ,Linkedin Answer ,Yahoo Answers .

Media centric communities like Flickr,Slideshare,Youtube

I have noticed that most of the time some specific member of network are more Vocal , enthusiast and involved than others. these user keep the conversation alive . a study says 20 % of Linked In users are answering 80% of Q . Yahoo Answer have similar pattern .

In old product/ technology centric paradigm we often call them power user or early adopters . There is no immediate material /objective gain form Answering someone’s Q or solving a problem on someone’s behalf . still people do it .
someone told me that “It’s not Just Altruism which promotes these guys to do so . another factor is that it satisfy their Vanity “. he even suggested that whole notion of option source is driven more by Vanity than by altruism . [i neither agree nor disagree with him , i never thought of Open source n Free software in that way ,however thats besides the point ]

I think that these Vanity users are Key to any social networks adaptation and growth . Who are these guys who write wikipedia articles ? i know only one such guy . My question is How can a upcoming startup ensure that it gets attention of Vanity users ? what appeals to them ? how can you attract and [more importantly] retain them .

can it be done by

Design ? ie: Having specific feature which uplift user’s social presence [ Linked in Recommendation,Fave count in slideshare , Testimonial in orkut, flickr ]

By reward ? : some incentive ie Cool Quotient index or Giving Visibility ,Profile of the day ,most read profile , max number of connection ,Hot count in Hot or not , Feedback grade in E Bay )

By some grading system ? (FANs in Orkut and Domain Expert status in LinkedIn, Crush Count in Facebook ,Technorati Rating )

whats your thoughts on this