A frontpage wiki is referencing to external blog content hosted somewhere else, similar to what Reddit is doing. The term URL spam is referencing to a behaviors of persons who are editing wiki pages with the aim to place advertaisment links on that wiki. The funny point is, that both are the same. Every frontpage wiki will look like linkspam. But without a frontpage wiki it's not possible to connect the community and to aggregate existing content.
The answer to the problem is to be aware that an aggregator wiki similar to Reddit will look as default like spam. It is only a question of the judgement if this perceived as a problem or as helpful. Let us analyze a neutral website like Planet gnome http://planet.gnome.org/ What is seen on the site is a collection of URLs which are referencing to wordpress, blogspot, google and gnome.org content. Planet gnome is basically an advertaisment website, founded with the aim of linkbuilding and traffic increasement of the referenced websites. Trying to explain to the newbies why planet gnome is different from URL spam / webring is not possible. It fulfills exactly this definition. The reason why the links doesn'T get deleted by the admin of the project is because the advertaisment feature is wanted. That means planet gnome was created exactly for the purpose of linkbuilding and rank manipulation in Google. The funny thing is, that at the same time, no ads are visible at the website. The user gets a clean interface combined with valuable content. That means, the website has reached the maximum amount of spam which is possible.
Sometimes the Open Source community is described as the opposite of modern capitalism. It's exactly the opposite. Linux and the ecosystem around it, sees advertaisment as their core ideology. Each blogger who is writing something about Gnome is trying to make advertaisment. He will increase the market share of Linux and the aim is to redirect the readers to other websites in which they can download the latest iso file from Red Hat or Ubuntu. The LInux ecosystem is overpopulated with ads. The idea of selling something is everywhere. The only exception to the normal world is, that the desired actions are not connected to money. The user can read the linked tutorial for free, the user can download the latest Fedora software without paying anything, and the updated podcast about a new Linux program is provided without charge in the Ogg theora format.