There really is no ideal keyword density IMO. Comparing the keyword density of top ranked sites on competitive search terms, you'll find they vary from 45% or more, down to 5% or less.
I really can't say that updatinf it more often will get yopu better ranking. I do believe that updating more often gets your site crawled more often, but more crawling doesn't = better ranking.
I readed your posting about meta tags, on page optimisation etc..
O knowed that stuff before, some were new, but, what is more important to obtain a better ranking?