I’d not necessarily wait for the new 5D – the existing one is a bargain, and I can’t see its price falling all that much further once the new one comes out. It’s an excellent camera (still my primary camera) and I regularly print to 20×30″ and higher.
The new one will have a 14 bit sensor, live view, larger and clearer LCD and an increase in resolution – probably to 16mp. All definite bonuses, but you’ll be paying the better part of 3k for it.
Image quality at Higher ISOs is something that Nikon have really excelled at with the D3, D700 & D300.
I know a few guys who adore the 5D but are really hoping that image quality at higher ISOs is improved on with the 5D replacement. Friend in work who does a lot of Semi-Pro Gig Photography stuff is really tempted to defect to Nikon due to the ISO performance.
Having strayed from Landscape photography of late I too would be looking for something that can perform well at higher ISOs.