I was stuck with the same dilemma, in the end I just went for it. Yes when the refresh models come out it'll be out of date, but in all honesty I don't care, it does everything I want to do and a hell of a lot more besides.
Unless you're the sort of person who HAS to have the newest gadget for e-peen purposes or you only want a Mac to show off with, I can't really see the point in waiting for a refresh. Especially when we have no idea what the refresh will involve and when it'll come, to be honest that it something about Apple that really irritates me.
In the end to me it seems very risky to wait for a new product you have absolutely no information on when you know the current product meets you needs. As an example, there are a lot of rumours (most probably not true) that the optical drive will be removed and the HDD possibly switch for an SSD (maybe with the ability to add another HDD in place of the optical drive). Now that may suit those who care only about speed and e-peen, but for me it'd be of no use whatsoever as I need storage space boot speed.
Anyway, I started to go on a bit so I'll end there. Just my 2p on the whole buy now of wait argument.