[quote name='defender']CheapyD has given me permission to install the phpbb points system. That could be the base for a means. Imagine that instead of posts to join a thread you have to have points. Points can be earned from posts, rewarded for starting good threads, or donated from other users. Just an idea.[/quote]
I hate to strike down your idea at the start, defender, but using points to determine eligibility in contests would fall under elitism and wouldn't work. The people with higher post counts would still end up on top by a long shot, even if a noob posted a couple of worthwhile deals. While "active members," as Scrubking defines them, should be commended for their contributions, contests should still be contests - equal opportunity to all - and not rewards or giveaways to the more active deal posters. Keep the contests as they are now, but if you wanted to offer an incentive to those with higher post counts, offer a little something extra to the winner if they can cite a deal that they've contributed. Noobs are happy because they still have a chance to win, and veterans are happy because there's an incentive to them for contributing to the site.
As for the point system, I think you could still use it, but in a different way. I have seen a few other message boards that give points as rewards for various things (i.e. hot posts, contests, referrals, etc.) that users can exchange for icons that appear by their usernames. One board (now out of existence) gave users virtual items that they could buy or exchange with others in a sort of RPG style. I don't know how well that idea might appeal to users here, but it was certainly an interesting concept.