First, a little background for those who may not be familiar.
cache is one of the Google Advanced Operators:If you include other words in the query, Google will highlight those words within the cached document. For instance, [cache:Google web] will show the cached content with the word "web" highlighted.I can't think of a way that this could affect SEO.
This functionality is also accessible by clicking on the "Cached" link on Google's main results page.
The query [cache:] will show the version of the web page that Google has in its cache. For instance, [cache:www.google.com] will show Google's cache of the Google homepage. Note there can be no space between the "cache:" and the web page URL.
I can't help to to recall a line from Hamlet, "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
There may be some unknown SEO-related effect from the Google cache, if not from the cache operator directly. I do occasionally see traffic from the Google cache.