The short answer is - if you need it, buy one now, whereas if you merely want it, then I suggest you wait until the next update (which will probably be in the new year). If finance is an issue, the I suggest that you try to get a refurb, which have all of the advantages of a new model - they come with Apple's warranty, have been individually tested - but merely have different packaging and are not usually the newest model if one has just been introduced.
Yes, significant changes are coming down the tracks, but that is the nature of technology - for such changes are always coming down the tracks, and what is cutting edge today is less so in a few months. The bottom line is that any computer - and every computer - designed by Apple is very good; buy one and enjoy it for now instead of torturing yourself; you can always replace it in a few years time with something more modern.
Cheers and good luck
