I find spelling mistakes or sentences that could be phrased better. Sometimes I change the rating too and I don't say anything about it. If there was a big change, like adding stuff, then I would probably do it yes. If you think though that you should mention it either way feel free to do it!

As for finishing something for the sake of finishing, I agree with Troy, I don't read /watch / listen to anything if I don't like it.

I agree with Troy and As the page turns.. it's your review. I don't often revise mine other than for typos or better phrasing or slight adjustment of stars. I kinda like to see what my thoughts were about the book at the time of reading.

I update for typos and grammar if I catch them. Other than that I tend to leave them alone. My early GR reviews are three sentences long and I've often thought of redoing them but life's too short to worry about them ... I have enough of a hard time getting my new reviews posted.