Pagetrading - Link exchange social utility | reciprocal link

Is someone ever thought how link exchange should work in a real world ?
well this discussion is open and here is my first opinion :

When someone have a links page to share , he might want to share this links with same subject websites. so he/her share this link on the web and on the other side, people that have common subject links may contact the former owner and establish a link exchange.

So i think it is much more complected . When you have a web page with 5-10 links+description and anchor text you may want to increase the popularity of this page , with search engine optimization process. when coming to link exchange it , you may want to achieve at least the same value of a web page in return , but what is that mean ?
here are few factors to consider :

1. Location of the page in search engines.
2. Which words are focused on this page ?
3. The PR of the page
4. how quality are the back links to this page.