I think this site should stay free for registered users as other forums and similar sites. Members donations should be accepted though. having one or two add on the page doesnt hurt that much and it generates much needed funds for this site!
Going forward, Pakwheels can introduce printed mag, i think will be a hit for its add and articles about the cars. It will also attract people who are not online! Online version can be subscribed with discount over the printed one!