Maybe some of these have been said - sorry if they have
User interface!
Users able to upload avatar
Show who they have voted for (maybe plugin for this)
More login options facebook, twitter, google again (Maybe plug in)
Send friends request (Maybe plugin but would be cool in core feature)
Admin Section
More stats - keywords, referrals.
Search bot - This would allow to search products I.E If you have made a link directory from this script you can make a section on the listed page to show the website products
Defo more SEO editing on listings, and across the whole site
Main site
improve search to include all keywords when searching
Make the premium listed stag clickable and then it would take you to the page with a list of PREMIUM ads only