It depends
I bought my iMac back in September 2009, just before a refresh, and yes, it was unpleasant to see that, when the new ones came out, I could have bought a stock model (old = my one) for approximatively 20% less.
However, if you want to wait for the latest model, you'll never buy one.
As said by other members, you have no clue what the new iMac will look like.
I preferred the form factor of the previous one, so ... good point.
Another aspect : if you buy a new one, you're never sure it will be without unforeseen flaws ... it's just such a pressure to get things to market in due time.
Having a model that's already marketed for some time means the flaws should have been vetted out.
Anyway, I would strongly advise the Applecare, especially on the latest/greatest/newest.
Looking back after nearly three years ... my frustration vanished, and I'm just enjoying a beautiful and nice engine. There is no difference between being satisfied, and being satisfied.
Not the most powerful ... but that wasn't a requirement.
Well, make up your own mind, take a decision, and accept the implications.