I was thinking of that as well.
Haswell will need a new socket 1150 and a new design of motherboard.
It's being said that the IGP will have at least 24 execution units. HD4000 has 16 and HD3000 only 12.
Apparently it will be available for desktops much later than expected.
I don't think there's a noticeable difference in performance nor temperature development between the 2500K and 3570K. And neither would 16GB RAM instead of 8GB make any difference as my system utilizes only up to 50% of my current 8GB RAM. Afaik the only differences between DH67CF and DH77DF are a new BIOS interface and quality capacitors. So you're right, a new system doesn't really make sense.
Although I don't expect a big difference, I still plan to get the SSD Samsung 830 (256GB) soon because it will be phased out from November 2012 onwoards to be replaced by the successor 840 Series.
The "Visual Bios" is somewhat worth to upgrade, but " quality " capacitors is not a reason in my opinion.
If you do care it, the Asus " ROG " series and Gigabyte " Sniper " series will be the much suitable choices.
I never use integrated video card so I won't be confused by HD 4000 or HD 5000, I just take it as a backup solution when my NVidia vga card can't work.
Samsung 830 uses TLC memory which I am doubting its reliability, so only I can say is " Good Luck ".