My site has PR 4 and is ranking No page 1 for 10 important keywords. The Title Tag, Description are not optimized to include Keywords. URLs are not seo friendly and a lot of further improvements can be made. I fear if I will change the current site data in order to further optimize my rankings may drop. What you say? Is it good idea to further optimize with hope of getting no1 position for all keywords?
If you're already hitting the first page, then it's probably not worth changes things. I'd just carry on with link building and trying to get good keyword-rich anchor text, and make sure any future pages you add have proper on-page optimization. If you have pages that are not ranking well already, however, fixing up the on-page optimization is a good idea.