Does the video plugin take advantage of dual core processors? I mean is it specifically coded to use both cores. I don't think that "normal" audio only Serato uses two cores, besides for building overviews. If not then the priority should be on processor speed not multiple cores. There are single core chips faster than dual cores for less money. If two cores are used, how how is the workload is split between both cores?

The Video app runs as a separate process to SSL so at the very least SSL will use one core whilst VSL uses the other.
I'm not sure I agree with your analysis of being able to buy single cores that are faster than dual cores.
Intel don't make a core 2 solo and the AMD Turion is no real competition.

also consider FX to utilize multiple cores.
if you've got 1 effect on 1 source, and another on another, plus a transition effect.... well, let's just say the more cpu cores you have to process these 2 or 3 effects, the better.

Both Scratch LIVE and Video-SL are multi threaded so will make use of dual core processors.