Please Help Me With Some Advice Before I Mess Up A Good Thing

A couple of years ago when I first started experimenting with IM, I purchased a domain in a highly competitive niche. Not knowing much about what I was doing, I put a "canned" adsense site up, and after realizing after the fact how competitive of a niche and keyword it was, basically forgot about it.

However, recently I noticed a spike in traffic, and see that this site is now ranked in the top 10(Yahoo) for this very competitive keyword. My issue is that with the level of targeted traffic I am now getting, this canned adsense site is clearly not the most effective means of monetizing. There are currently 318 pages indexed in google, but all are generic article based pages with adsense.

My question.....will I lose my search engine ranking if I put a different site(using everything I now know about how to monetize the traffic more effectively) up at that URL.....is there a way to pull this off and maintain the high ranking. This is made more complex by the fact that the site sitting at the URL now is one of those canned generic adsense sites that is not really modifiable into anything decent. I'd want to put up something completely different

Thanks for Your Help Warriors