Nope. Many computation problems are either impossible or very inefficient to do in parallel. You also can't take your second point ("paying the same price") at the same time as "more processors of the same level or model". Not only are you not going to get more processors for free, they require more space, more power, more connections, more everything. It is not at all clear that more processors is the ideal approach.
A general purpose processor can, given enough time, pretty process anything. One very simple way to use parallel processing in a camera design is to use the processors as stages in a pipeline. eg the first shot uses the first free processor, while a second shot can start using another processor while the first is still in progress.
I do not know what architecture Canon use in the DIGICs, but I would not be surprised if it follows this model - not least because it is an architecture where adding more chips can be used to add more FPS or larger larger burst sizes.
However, the price you pay for this is power consumption (battery life), which rises linearly with the number of cores actively being driven.
General purpose CPU cores are always less power efficient than dedicated circuitry, so an alternative is to add more specialised circuitry instead. This gives a better performance and power consumption, but is less flexible and harder to get right as it fixes the algorithms in hardware (not Canon seem keen to provide feature updates in firmware anyway).
In short there will be a balance between the number of cores and the dedicated logic, which will largely be driven by engineering, time and cost constraints. A large number of cores does not automatically mean a faster processor (but it certainly means a more power hungry one).
So instead of worrying about how it works, worry about how well it works and ignore the marketing hype...