Here's the ultimate SEO dilemma…you have a page on your website that performs well on SEO, but you know it stinks.  It has old-school keyword stuffing, a lousy link or two, or is just not the quality content that you produce now.  Should you leave it alone or revise it?

School of thought #1:  If it ain't broke, don't fix it.  In other words, until Google tells you via a page penalty that the page stinks, leave it alone.  It's hard enough to get a page to rank, so why fiddle and fool with something that could result in a lower page ranking.

School of Thought #2:  Yes, dammit, by all means improve content where you can.  There is every likelihood that you're considering a rewrite not just because the page is spammy, but because it's not converting.

If a page is content-lousy, but still converting, my gut tells me to leave it alone until it stops converting at a high rate.  But if that page has stopped converting, that is indeed the time to take the plunge and go for a rewrite.
Heather Lloyd-Martin of SEOCopywriting.com offers some tips when rewriting content.

•    If the content has more keywords than you normally use in your current writing, either add more content to thin the keyword ratio or cut one or two and see how the content stands after that.
•    Does it seem the page is written for Google and not the site visitor?  Put yourself in the visitor's shoes, then rewrite the copy.  Can you keep a few of the keywords while reinventing the copy?  Let's hope so.
•    Test the new content.  If you have a major drop in rankings, you may have to switch back, add a few more keywords or make some additional revisions.

The key in rewrites is the conversion rate.  If you have high rankings, but no conversions, what do you really have?  On the other hand if you have a great page, but still no conversions, that's temporary.  Because if you've created a compelling piece of content, it will resonate and rank eventually.