New editions worth it?

Hi, I'm hoping to study Archaeology and History at university and have been doing some reading beforehand. A family member bought me a second hand copy of an essential and well regarded book that is on the reading list but I've since discovered that the copy I've been given is 12 years out of date and the newest edition is the sixth one, whereas I have the third. Does it really matter if I have an older copy? Of course I realise it has been 12 years which is kind of a big jump. I just feel I would prefer my own copy rather than borrow one and it would also be a shame to drop the book I have. The new edition is £24 at its cheapest. Any helpful comments would be greatly appreciated!