Discussion: Do you re-rate books?

I used to read and rate books no problem, I just rated a book whatever I felt like at that particular moment. Since I've started blogging though it seems to be a bit more complicated...

One of my biggest problems with rating and reviewing books is that I often feel the need to go back and change my initial rating. So does this just make me indecisive? Who knows, but let me explain. 

Reason number 1: I rated it too hastily the first time.  I always rate books higher initially then I would if I waited a while. Part of a rating for me is how much of an impact the book had on me. Do I remember it? Was it insightful? Did it teach me life lessons? If I don't give myself this breathing time then I might think it was impactful, when in actual fact the only reason I think that is because I've literally just stopped reading it. While I know I make this mistake, I continue to do it...

Reason number 2: I compare a book to other books. On more than one occasion I've been going through my Goodreads and noticed that I've rated two books the same when I know full well I enjoyed one more than the other.  For example, recently I gave The Daughter Of The Pirate King 4 stars, I also gave 4 stars to Windfall, but I know I enjoyed The Daughter Of The Pirate King more. However, I don't think Windfall deserves a 3.5 because some of the books I've rated as 3.5 I didn't enjoy as much a windfall. Do you see my struggle here...This isn't an isolated incident either, so what do I do with these books? What do I rate them...

Personally I always feel slightly guilty for re-rating a book, like I'm going against my post book self by changing it. Part of me wants to change my ratings because that's how I feel now. But then there's another part of me that thinks, if that's how I felt after reading that book then shouldn't I leave it alone. Is this not my 'true' rating...So let's discuss. Do you re-rate books? Or do you ever get the urge to? Do you even rate book, I know a lot of people don't!