[Edit - oops - just noticed the original post was ancient :-| ... ]
Consider using one of the two features already built into the site: the favorites star, and your profile (which shows your history in several ways.) Your browser also has a history, bookmarks, etc.
IMO, if a post warrants your reconsideration via an altered vote, the topic / question is presumably one you would already be interested in enough to pay attention to in the first place. That's what the favorite star is for - it is an effective mechanism when used properly.
But there is another angle to consider: reducing confusion.
On other Stack Exchange sites, when an edit changes the meaning of the original question significantly, the answers and comments can loose context or even become completely inappropriate. The moderators often catch such edits, but it also puts more work in their work queues.
A conscientious poster should be aware of minimizing their work load.
So if an edit enhances and adds to the meaning, that's great. But if an edit were to make things less clear, alter the course of comments and answers, or just generally make it "fuzzier," then it would perhaps be better to post a new question and await new answers. (This approach is based on multiple comments and answers I've received in related topics elsewhere.)
Although your question has many up votes, I don't think the advantages of your request would off set the computing overhead required to implement the suggestion.
So, please do consider using what we have already.