Editing Old Posts & SEO

I’ve got a site that is doing very well and brings in a lot of search traffic.

However, looking through the stats, it seems the vast majority of my traffic is brought in by 20% of my posts (80/20 rule, anyone?)

I have a lot of early posts that I did years ago before I knew anything about SEO and optimization.

They’re not optimized in the slightest (not even title and URL optimization), but they’re solid posts.

So I’ve been considering editing these old posts and optimizing the heck out of them. Couple of things I’ve been considering:

• is this a good idea from an SEO perspective?
• my site is very well interlinked. I know that if I change the URL of a post, then the posts linking to it will display a broken link. Any plugin that will re-direct those links after I update posts and change the URL on some?