I'm in year 11 (GCSEs this summer), and I guess it depends on what you're aiming for. If you're heading for straight A*, then regular revision will make it sooooo much easier.. (I wish I did!). Maybe just reading through the notes you made in class, or a revision guide or whatever, no need for hardcore revision. And yeah, year 9 is a good year, enjoy it, don't even think about stressing now!
Apparently though (but don't quote me on this) GCSEs are going to be considered more important, since most A levels are going linear, so basically the only solid grades unis have to look at are your GCSEs. :/