Altho you may consider it "informational", its still spam. Considering the probs we deal with as a result of ppl using scripts/addons/plugins they dont understand fully, it wouldnt make much sense to then allow ppl to post their urls here. Anyone having a prob with something they found here would be bound and determined to blame it on mIRC.
As for a section on third party plugins, there are numerous sites that inspect the ones they allow to cut down on those that contain trojans/cause probs. That isnt the purpose of this forum and quite honestly i see no need for it here.