Have you looked at the Gumstix Overo COMs? COM = Computer On Module. They have a dedicated camera interface (J5). Beagleboard may have this as well, as it is the same OMAP35xx series processor.
If you want to roll your own, there are many, many microprocessors with camera interfaces. Freescales i.MX series of devices (i.MX31, i.MX51, etc.), the OMAP processors I mentioned above, Atmel has the AT91SAM series... What other features do you need?
You can fake this pretty effectively in Altium Designer.
Altium has what they term "Recyclable Schematics" - Schematic layouts that you can paste into larger schematics and treat as components.
Duplicating the PCB end is a bit more work, but definitely doable (I've done it). Basically, you route the DC-DC on one board, and then simply copy-and-paste the design into whatever new board you have. This will move the component footprints, and traces, but not the nets. Then, assuming you have the corresponding schematic entity, the next time you synchronize the schematic and PCB, Altium will match the free-floating footprints to their schematic entities, and add the netlabels to the existing copper.
Alternatively, assuming you are OK with not being able to edit the DC-DC layout in situ (on the PCB), you can just paste the layout into a footprint library, and define where you want input and outputs to be.
In this case, you would edit the library file, and then propagate the changes out with the "Update from PCB libraries". You can also modify the primitives of a component once it has been placed, but changes there will not propagate back to other places you have the component.
Third, Altium can embed one board into another - I use it for panelizing things, but I think you could probably also use it for embedding one functional section into another. It wouldn't tie into the schematic, though.
It's worth noting that I do the first two of these regularly at my job (usually with FTDI USB-Interface circuitry) - It's definitely a viable approach.
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Given your baseline of 1GHz ARM you are looking at a multilayer board (8 layers say) with a high pin count BGA package. An AM3539 is a 324-Pin PBGA package. Assuming you don't go package on package for the memory, you are looking at an awful lot of high speed interconnects, all of which have to be balanced and impedence matched. You'd start with a 5 grand licence for Altium Designer or something similar.
You can have a look at the hardware platforms like the Beaglebone and the Pandaboard which will give you an excellent idea of the scale involved. There are some terrifying videos on YouTube (example) showing you the routing involved with DDR3.
What I'm doing currently is designing a baseboard around a SoM - a system on module (A Gumstix). All the horror is taken care of, yet you have a lot of low level access to pins.