A64 is better with games, P4 is still better with video (although the gap isn't as large as it was in the Athlon XP and P4 days).
The advantages of the A64 on socket 939, lower power draw, less heat, and (in comparison to a s478 P4) a direct upgrade path to dual-core A64s outweigh the (IMO) single benefit of a P4 (Northwood or Prescott), faster performance with streaming media (e.g., audio or video encoding). I think the dual-core Pentium D/Extreme that Anandtech previewed required a new motherboard to work, whereas you can buy a s939 A64 MB now and simply plug in a dual-core A64 when they come out in a few months.
AFAIK, the Venice A64 core adds SSE3 and some other tweaks (higher clock speeds, improved memory controller speeds for >2GB RAM), but consumers a little more power than the current 90nm revision (Winchester?). It doesn't sound important enough to wait too long, IMO, but that's from the POV that you'll upgrade to dual-core in a year or so anyway.
Does Venice offers any tangible clock-for-clock improvements over Winchester, or is it mainly to boost clock speeds? I skimmed a review, but I don't remember it outperforming a similarly-clocked Winchester core.
Edit: The A64 3000+ is closer to $150, no? Or am I thinking of the OEM version.