I struggeld with this a bit myself, but ended up buying a mini on Saturday.
I wanted to edit video and my old macbook wasn't up to par. What made me leap was the fact that it really had everything I needed on it. Sure there will be a GPU boost and maybe better wifi on the next model, but I'm still on 802.11G at home and N at work. The GPU would be nice but I doubt whatever it is will really give me a significant gain in video editing. But I also feared that Apple may remove the firewire jack on the next model and I need a firewire jack to capture my old DV tapes. My macbook didn't have one.
The only other thing the new mini may have is more stock ram. But with the cost of ram going up, that may not happen either. Plus I plan to put 16GB in this machine anyway. So even if they bumped it to 8GB, that would still be 8GB of ram just sitting in my closet collecting dust.
Plus buying now meant getting the mini for $50 off since many retailers have it on sale now.
But it also depends where you are coming from. I was coming for a 2008 macbook with a 9400M in it and C2D chip. So no matter what, this new mini is an upgrade for me all around.