I think its in your best interest
We are at least 3 to 4 months away from the release, might as well wait it out unless you desparately need a computer to use right now and don't have one.
I personally am waiting, but I don't have any choice, since my vacation leave doesn't come in effect until late November which is when I plan to purchase my first iMac.
I will also be going with the base model 27 inch based on my needs, Internet, email, office productivity, social networking, watching movies, manage my photo collection, some light video editing, like what I record on a smart phone and so fourth. I want the 27 inch because of the screen real estate, the ability to upgrade the RAM at my leisure, so its future proofing in a sense.
I don't necessarily need the top end, but I do hope in the next revision Apple will at a minimum upgrade the video card with a minimum 1 GB of vRAM. It would be nice to also have a Fusion drive just for the boot performance, launching apps and general task. Using a Windows 7 based desktop right now with an SSD, its kinda hard going back to a spinning drive, even on a very fast computer (CPU, RAM).
Taking into account this a computer that doesn't have much upgradable components, its a significant investment, so if you plan to buy, make sure it comes with the components that you will be satisfied with. I use my systems till they die. I have an Acer laptop going 7 to 8 years so far with Windows 8, it boots sometimes when it feels like it, but its usable, and I have a 5 year old HP which is still going strong which I use as my iTunes machine. Hope to consolidate all the content on both into a single desktop.
I also forgot to mention, in addition to improved Graphics, the next Mac is likely to include features such as faster 802.11 AC wireless, improved PCIe Fusion drive for added performance. So these are some things you might want to add to your consideration.