Dream sequences are pretty much an overused trope at this point, it's been done so many times, and it doesn't really offer anything more than instant self gratification. It can work if it makes sense in the story, if it's written well (yes, even dream sequences need to be written well). This is of course my personal opinion, but I've always preferred proper relationship build-up before finally getting to the "main prize", that doesn't mean there shouldn't be sex at all before the 10th update, it just depends on the character. As long as it makes sense and is written well, feels natural and believable rather than forced and out of the blue, anything goes really.